p-winds

This is a beta test of the version 1.4.1 of p-winds. There is quite a bit of new features. The code now calculates the density profiles of exospheric metals! Here is the changelog:

• New module: carbon.py is used to calculate the distribution of neutral, singly-ionized and doubly-ionized carbon in an exoplanet's upper atmosphere.
• New module: oxygen.py is used to calculate the distribution of neutral and singly-ionized oxygen in an exoplanet's upper atmosphere.
• New module: lines.py stores spectral line information. This information was previously stored in microphysics.py, but was moved to avoid bloating the latter module. Please pay attention to this new usage of microphysics.py! As always, check the documentation to learn more.
• helium.py now includes a function ion_fraction() that calculates the ion fraction of helium more quickly than the population_fraction() function.
• New examples in the documentation: Roche lobe effects and exospheric metals.
• General bug fixes and updates to docstrings.

We encourage users to test this beta version and report bugs in the GitHub issues. As always, please check the documentation of the code for guidance on the functions parameters!