NAMD parsers

In line with the overall API proposal, we want to have parsers for each of the major MD engines, and eventually have coverage for all of those in use. Since there are essentially two types of estimators (TI and FEP), each packages needs a parser for:

1. Extracting reduced potentials u_nk from output files (for FEP).
2. Extracting derivatives DHdl from output files (for TI).

This issue is the nexus for discussion for such parsers for the NAMD package. If you have existing parsing code for this package, comment below and we can begin adapting it into the parsers outlined above in a PR.

[davidlmobley]

@orbeckst - we’ve not used Sphinx yet, so this is helpful. yet another argument for a general “best practices for code development” writeup. 😃

[orbeckst]

Good, feel free to grab alchemistry/alchemtest#17 !