Pytest-plt

**Changed**

- Python 3.5, which is past its end of life, is no longer supported. ([\26](https://github.com/nengo/pytest-plt/pull/26))

**Fixed**

- Config options are now properly added to Pytest, eliminating a warning that was raised if a config option was set. ([\26](https://github.com/nengo/pytest-plt/pull/26))
- Handled multiple outputs when mocking out `plt.subplots`. ([\29](https://github.com/nengo/pytest-plt/pull/29))

**Added**

- Added the ability to save plots as pickle files using the `.pkl` or `.pickle` extensions with `plt.saveas`. ([\23](https://github.com/nengo/pytest-plt/pull/23))

**Fixed**

- We now use Windows-compatible plot filenames by default. Colons in plot filenames are replaced with hyphens. Filenames specified through `plt.saveas` are not modified. ([\17](https://github.com/nengo/pytest-plt/issues/17), [\#21](https://github.com/nengo/pytest-plt/pull/21))

Initial release of `pytest-plt`! Thanks to all of the contributors for making this possible!