- Completed total transition to and validation of `_hybrid1()` in the `mp1` class
- Added `d_s()` to the `mp1` class
- Standardized `igmix`, `ig`, and `ig2` classes to use the same argument parsing rules
- Standardized `igmix`, `ig`, and `ig2` inverse property routines `T_s`, `T_h`, `p_s`.
- Added filtering capabilities to `info()`
- Added `atoms()` to all classes to retrieve atomic composition data.
- Updated the `dat.updatefiles()` function to correct bugs in Python 3.
- Changed `PMConfigEntry.apply_default()` to `restore_default()`
- Changed `PMConfig.write()` algorithm to deal more gracefully with appendable entries.
- Added function type 0 to `mp1._satfit` for future melting line support.
- Added `mp.N2` and `mp.CH4` multiphase models.
- Added `R()` and `mw()` to the `mp1` class.
- Adjusted all multi-phase R-values to agree with Ru / mw to numerical (double) precision. For most properties, the change will not be noticeable, but it brings some into better agreement with published values. In all cases, the change is on the order .01% or smaller.