Separate out original SIMPOL.1 from modified Meredith et al. methods

[Aariq]

• Adds a new logical argument to simpol1() and a new method to calc_vol().
• Adds SMARTS strings for primary, secondary, tertiary, and total amides.
• Removes catch-all amides coefficient from Meredith method and enables amides in SIMPOL.1 method

This PR assumes that the difference between meredith and simpol1 is just the additional coefficients added for phosphate and sulfur containing groups. To fully reproduce the results in Meredith et al. 2023, users will need to install a legacy version of volcalc

[Aariq]

@KristinaRiemer, when you get a chance, would you take a look at the documentation changes and make sure they make sense?