Fix absence of LONG_DESCRIPTION
isolibrary.LibraryBuilder creates isofiles

This update:

- Creates the isolibrary module for working with isochrone libraries
- Creates the LibraryBuilder to aid in constructing StarFish isoc libs
- The _build_isofile() method helps create isofiles from *parsed*
  padova isochrone grids (that is, from isochrones split into
  one Age/Z per file). *StarFISH has an awk script that can be modified
  to do this; eventually we'll do it internally.*
- The install() method creates the isofile *and* runs `mklib`.