REL: v3.8.0

Highlights of this release include:

- Type hints for most public APIs
- Many improvements to Mathtext
   - Addition of ``\boldsymbol`` command
   - Additional sizable delimiters
   - Documentation improvements
   - ``\substack`` command
   - ``\middle`` delimitier
   - ``\mathbfit`` for bold italic text
- 3D plotting improvements
   - Specify tick/axis label positions
   - Improved text for coordinates in interactive sessions
   - Ability to share view angles
- New plotting method ``ecdf`` (empirical cumulative distribution function)