Nexpy

* Allows LMFIT parameter expressions to be edited to include any parameters in a composite model.
* Allows LMFIT composite models to combine different models with the standard binary operators, *i.e.*, +, -, *, or /.
* Allows different components of a composite model to be combined flexibly when plotting the model calculations.
* Allows data to be masked before fitting. Masked points are selected either by a right-click zoom or, if the **mplcursors** package is installed, by double-clicking on individual points.
* Uses the current plot limits to define the data included in initializing and fitting parameters in the Fit Panel.
* Updates saved fits to include the composite model definition and parameter expressions.
* Adds a BoseFactorModel that, when multiplying another lineshape, *e.g.*, a Lorentzian, obeys detailed balance for negative energies.
* Adds the option to rename a copied NeXus field or group before pasting it.
* Adds the plot legend when using the `mpl_plot` function to plot an existing NXPlotView window to another Matplotlib figure.
* Adds options to use data paths as legend labels in the Customize Panel.
* Adds grid parameters to the Customize Panel for 1D data.
* Adds the option to change the grid alpha value in the Customize Panel.
* Adds extra linestyles to the Customize Panel.
* Modifies the color cycle to match the current Matplotlib style.
* Allows a size-1 array to be plotted.
* Adds a "Open NeXpy Issue" button to the Log Window.
* Adds a `save` function to NXPlotView to save the current plot to a file.
* Ensures that shapes are removed from the NXPlotView `shapes` list when they are removed from the canvas.

* Adds support for plotting weighted data. If a weights array, [as defined by the NeXus standard](https://manual.nexusformat.org/datarules.html), is present, a new "Plot Weighted Data" option will plot the signal divided by the weights.
* Adds support for adjusting the aspect ratio when `aspect=equal` is selected. If the axis field has an attribute named `scaling_factor`, its value is used to correct for the absolute values of the axis units. This is useful for axes which represent lattice vectors or reciprocal lattice vectors, whose values are multiples of unit cell parameters.
* Adds support for applying a skew angle when `aspect=equal` is selected. If a NXdata group of rank 3 has a group attribute named `angles`, the values are used to define the skew angle between two axes when the corresponding value is not 90°. For example, if the `angles` attribute is set to `(90.0, 70.0, 90.0)`, a skew angle is applied to plots where the x-axis and y-axis are dimensions 0 and 2, respectively.
* Adds a new "Open Startup Script" option to the Script menu to allow the startup script to be edited.
* Adds the option to select the available Matplotlib styles in the "Edit Preferences" dialog. A new "Publication" style, with enlarged fonts, is added to the list.
* Adds support for customizing the color of "bad" pixels in the Customize Panel.
* Adds a new NXPlotView function function, `mpl_plot`, which reproduces the current plot, preserving its formatting and legends, in a Pyplot axis, to facilitate its inclusion in Matplotlib layouts created by, e.g., `subplots` and `GridSpec`.
* Removes NeXus files from the tree if they are in a remote directory that is no longer accessible.
* Removes the legacy Pseudo-Voigt function in favor of the model provided by the [LMfit](https://lmfit.github.io/lmfit-py/) package.
* Fixes a bug where file locks are not cleared when shutting down NeXpy.
* Fixes a bug through which a panel opened in a plot's Projection Tab is linked to a different plot.

* Adds a pull-down menu to the Projection Tab for selecting which panel to open (Projection, Limits, or Scan).
* Adds support for LMfit forms, which allow some fitting models to be customized. This requires LMfit v1.0.2.
* Confines the fitting range to the x-limits of the parent plot. This can be changed with the "Reset Limits" button.
* Removes legacy fitting functions that duplicate LMfit models.
* Makes the Script menu display subdirectories hierarchically.
* Adds new Matplotlib color maps - two qualitative maps (tab10 and tab20) and a gray-scale divergent map (divgray).
* Fixes issues caused by changes in Matplotlib v3.4.0.
* Fixes a plotting bug when a scan variable is not set in the Scan Panel.

* Fixes an incompatibility with Matplotlib resulting from code changes in the version 3.3 release.

* Fixes version requirement for the nexusformat package.

This release is the first to require Python 3.

* Speeds up the loading of NeXus files by limiting recursion of group reads to two levels in the hierarchy by default. Lower levels are automatically loaded when they are referenced, e.g., by expanding the tree.
* Adds "Edit Preferences" to the File menu to allow NeXus constants, e.g., defining memory limits, string encoding, etc, to be saved for subsequent sessions.
* Adds the ability to restore all the files loaded in the previous NeXpy session, either using "Restore Session" in the File menu or using the -r switch.
* Adds "Reload All", to reload files changed by external processes, and "Remove All", to remove all currently loaded files, to the File menu.
* Adds a menu item "Show All Limits" to open the Limits panel and add all current plots.
* Improves the Import Text option to give greater flexibility in setting signals, adding headers, excluding columns, etc.
* Improves the Export option to allow export to NeXus files and to allow additional NXdata fields to be exported.
* Adds support for using the `interpretation` attribute to identify RGB or RGBA data and plot as images automatically.
* Implements manual garbage collection to prevent system crashes caused by automatic disposal of PyQT objects outside the main GUI thread.
* Fixes a bug when plotting external fields.
* Fixes a MacOS bug that makes the menus unresponsive when first starting NeXpy.