Nexpy

* Adds `nxopen` as an alias to `nxload`, returning the NeXus file tree as a `NXroot` object.
* Adds context manager functions to the `NXroot` class. This allows the use of `with nxopen(...) as f:` to open NeXus files in a similar way to the standard Python `open` syntax. In this example, `f` is the `NXroot` group of the NeXus file.
* Allows `NXroot` objects to be sorted by their internal names.
* Allows `NXlink` objects to be equated when they share the same target.
* Fixes a bug when plotting 2D data with the 'tab10' color map.

* Allows a lock expiry time to be set, after which locks are considered stale and automatically cleared. This defaults to 8 hours.
* Adds new functions, `nxgetlockexpiry` and `nxsetlockexpiry` to query and set, respectively, lock expiry times
* Fixes an issue that sometimes prevented a new lock from acquired in nested contextual menus.
* Catches exceptions caused by the deletion of a NeXus file that has already been loaded.

* Fixes an issue with missing links in external files.

* Fixes an issue preventing NeXus trees from being pickled.
* Fixes an issue when using special formatting instructions to print NXfields.
* Officially advertises support for Python 3.10.

- Fixes a bug preventing plot titles and axis labels of image plots from being changed by the Customize Panel.

- This version removes 'tifffile' from the NeXpy code because it is now available as a separate PyPI package or as a conda installation. The resulting package is pure Python, making it easier to distribute versions for multiple operating systems.
- If modules are not available when NeXpy is launched, _e.g._, lmfit for fitting or tifffile for importing, they may be installed during a NeXpy session before the user tries using them again.
- This fixes an incompatibility with the latest version of spec2nexus.