Nexusformat

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. Fully recursive loading can be restored by calling the `nxsetrecursive` function.
* Adds support for writing HDF5 soft links without the `target` attribute by adding the a boolean keyword argument, `soft`, when creating an NXlink. It is set to `False` by default.
* Adds support for the `interpretation` attribute. If the NXdata signal field has the attribute set to 'rgb' or 'rgba', it is plotted as an image by default.
* Changes the default text encoding to UTF-8, rather than using the system default. This is required by the NeXus standard.
* Fixes a bug in the `rename` function preventing affected `signal` and `axes` attributes from being updated.
* Fixes an issue with setting a NXfield dtype of kind 'S' without specifying its length caused by changes in h5py v3.

* Makes smart indexing of NXfields consistent with NumPy arrays.
* Improves handling of scalar values in NXfields derived from masked arrays.
* Improves formatting of floating point values.
* Improves floating point precision when computing axis values.
* Catches import errors when the readline package is not installed.

* Improves synchronization of fields or groups within a linked group. It is no longer possible to modify such items directly from the linked group.
* Improves detection of data for default plots within NXsubentry groups.
* Adds new NXgroup functions, `get_default` and `set_default` for setting and identifying default plots.
* Adds new `any` and `all` functions to NXfields, to mirror the respective NumPy functions.
* Adds new `ndim` and `shape` functions to NXdata to return the respective properties of the signal.
* Fixes a bug that allowed attributes to be updated when a NeXus file is locked.
* Fixes a bug when testing the existence of an externally linked path within a corrupted NeXus file.

* Adds new NXfield query functions required by NeXpy.
* Fixes a bug that allows attributes to be modified when a file is in read-only mode.
* Improves initialization of external links when opening files.

* Adds optional file locking to protect NeXus files accessed by multiple processes.
* Adds a context manager to open and close NeXus files before and after multiple read/write operations.
* Allows the use of all h5py.Dataset keyword arguments when creating a NXfield, such as `maxshape` and `fillvalue`.
* Adds a NXfield `resize` function to resize arrays in place within the bounds set by `maxshape`.
* Modifies the NXgroup `copy` function to enable use of h5py.Group copy to copy between files. It accepts the same keyword arguments, for example to embed externally linked data in the copied file. Note that the `copy` function no longer returns a deep copy of the group, but using `deepcopy` directly provides the same functionality.
* Allows h5py.File keyword arguments to be used in the `nxload` command.
* Adds a SciPy interpolation function to the NXdata class to smooth one-dimensional data.
* Adds autocompletion of NeXus group dictionaries as an IPython extension.
* Adds `nxduplicate` command-line script for duplicating NeXus files with h5py keyword arguments.
* Adds `nexusformat` command-line script to return the package version number.
* The `len` function now returns the size of the first dimension, for compatibility with NumPy and h5py.
* Stores modification times in NXFile instances to allow modifications by external processes to be detected.
* Improves docstrings for all functions.
* Adds a suite of `pytest` functions and implements Travis-CI checks on Github.
* Fixes a bug when adding two NXentry groups.
* Fixes a bug where attributes are added to more than one group.
* Fixes a bug with determining valid plotting axes in files created by Mantid.
* Improves error messages for missing external links.

* Fixes a bug with plots using Pyplot.