NG15yr Analysis, EQUAD Redefinition and Empirical Distribution Tweak

This version makes a major change to the way that the EQUAD parameter is modeled. Enterprise has officially broken backwards compatibility, renaming EQUAD parameters to either:

• t2equad to follow the timing package (Tempo, Tempo2, Pint) definition of EQUAD, i.e. sigma^2_T = EFAC^2*(sigma^2_TOA + EQUAD^2)
• tnequad to follow the TempoNest definition of EQUAD, i.e. sigma^2_T = EFAC^2*(sigma^2_TOA) + EQUAD^2

In addition, a number of fixes to the empirical distribution submodule were made as well as the full complement of solar wind models added. See below for all of the details.

What's Changed

• Fix empirical distributions and hardcoded gwb prior draws by @AaronDJohnson in #156
• fixed simulated psr bugs, added params to specify spectrum priors by @astrolamb in #158
• More changes to empirical distributions by @AaronDJohnson in #157
• Use svd by @AaronDJohnson in #160
• KDE empirical distributions by @meyers-academic in #159
• fix white noise in the models for non-NANOGrav PTA analysis by @siyuan-chen in #164
• add fix for timing model by @siyuan-chen in #162
• add chi square functionality and tests by @Hazboun6 in #166
• Solar wind models by @Hazboun6 in #167
• New Equad by @Hazboun6 in #169
• added kwargs for logL, logp in sampler by @astrolamb in #170
• Version2.4.0 by @Hazboun6 in #171

New Contributors

• @meyers-academic made their first contribution in #159

Full Changelog: v2.3.4...v2.4.0