TidalPy version 0.3.4

Beta release of TidalPy version 0.3.4

Major Changes (see changes.md for a more complete list of changes):
* Added TidalPy.modes.multilayer_modes.py module to offer simplified calculation of multilayer tidal
heating.
* Added GridPlot class to quickly make grid-like matplotlib figures.
Checkout TidalPy.utilities.graphics.grid_plot.py
* Added Cartopy dependence.
* Can now make cool projection maps! Added basic functionality to TidalPy.utilities.graphics.global_map.py.
* New jupyter notebooks to showcase map projects and GridPlot functionality.
* Improved performance on both mode and non-mode tidal potential functions by at least a factor of 3. If used
correctly these can be nearly 100x faster.
* Added a new obliquity version of the mode version tidal potential.
* Stress and strain relationship for multi-layer tides now allows for arbitrary rheology.
* Created a single multilayer solver to handle an arbitrary layer structure.
See TidalPy.tides.multilayer.numerical_int.solver.py
* Stress & Strain relationship now accounts for arbitrary rheology.
* Created a single multi-mode solver for multilayer problems. See TidalPy.tides.modes.multilayer_modes.py
* TidalPy now defaults to using the frequency dependent zeta versions of Andrade and Sundberg rheologies.
* This was done to avoid issues with real(complex_comp) at zero frequency which happens in multi mode
calculations.
* Added numba-safe version of multilayer calc