Faster get_separatrix function for equatorial pro- and retrograde orbits

[Philip-Lynch]

Main Update:

• get_separatrix() now considers if x is either 1.0 or -1.0 and root-finds the separatrix_polynomial_equat instead of separatrix_polynomial_full with appropriate bounds.
• In solver(), epsrel has been changed from 0.001 to 0.00001. This increases accuracy while not making the solver that much slower than before.
• Overall, get_separatrix should now be an order of magnitude faster in the equatorial case.

Minor Updates:

• Added .gitignore to stop git from tracking files from building and using the code.
• Updated FastEMRIWaveforms_tutorial.ipynb to get comment out references to multiple threads as this does not work on my machine with an M1 chip
• Updated README.md in accordance with the contributing guidelines

[Philip-Lynch]

Major Update:

• Have now added expressions for the fundamental frequencies specialised to the equatorial plane. Provides the exact same results while running slightly faster than before and does not have numerical issues for x = 1 or -1.

Minor updates:

• Updated .gitignore to ignore more files created when building FEW
• Changed the version number in README.md back to 1.4.10 as the updated version number caused issues when using the example notebook when finding and downloading files.