Xpecgen

- Target material can be selected. However, note the caveats in the readme.
- Expanded available material data.
- Handle calculation exceptions in the GUI.
- Add calculation interruption in the GUI.
- Display element name in GUI.
- Fix a bug (16).


See the [GitHub repository](https://github.com/Dih5/xpecgen) for more information.

- Fixed the overall e_0 dependence factor which was wrongly introduced in v1.1.0. This affected only superposition of spectra where the relative norm is relevant (e.g., non-monoenergetic source as done in a demo).

See the [GitHub repository](https://github.com/Dih5/xpecgen) for more information.

- Command line interface added.
- Allow to load the xpecgen module and perform calculations if matplotlib is not working.

See the [GitHub repository](https://github.com/Dih5/xpecgen) for more information.

- ~~X ray distributions are provided with no overall e_0 dependence factor. This allows for studying the production done by non-monoenergetic sources~~ (bugged, fixed in v.1.2.1).
- API support for general grids (calculate_spectrum_mesh function).
- API support for positive linear combinations of Spectrum instances.
- Fix a TK-related bug that appeared on some configurations (14).

See the [GitHub repository](https://github.com/Dih5/xpecgen) for more information.

- Fixed a discrete-component related bug (6d6b4d5a974672508930897b9ec7d93fe304f913).
- Documentation improved.

See the [GitHub repository](https://github.com/Dih5/xpecgen) for more information.

Added python 2 compatibility.


v.1.0.0
First xpecgen release.
- API considered stable
- Norm-related functionality added to the GUI.
- Minor fixes.