Release 0.3.1

Added

• [docs] Use example gallery to show examples.
• [cpp] Implement serialization/deserialization for piecewise poly trajectory.
• [cpp] Provide Python bindings for PiecewisePolyPath, TOPPRA and constraint classes.
• [cpp] Construct piecewise poly as a hermite spline.
• [cpp] Add varying joint velocity limits.
• [python] [#117] Provide an option to allow Python 2.7 usage
• [python] [#117] Post-processing is now done via parametrizer classes.

Changed

• [python]Add some type annotations to parameterizer.py
• [python]Support older interpolation method.
• [cpp] Minor improvement to PiecewisePolyPath.
• [python] Implement ParametrizeConstAccel to allow reparametrize path.
• [python] Parametrization output accessible via ParameterizationData class.
• [python] Remove useless scaling in parameter computation.
• [cpp] Clamp velocities to be within controllable sets.
• [ci] [#117] Improve CI pipeline to test on several python versions
• [ci] [#139] Automate publish to PyPI server