Lsstdesc-gcr-catalogs

This release is the first Release Candidate of GCRCatalogs v0.8.0.

Compared to v0.8.0-beta, the protoDC2 catalog has been updated to v5.0.

This release
- fixes the behavior of truth reader: it now returns numpy arrays that correspond to the correct dtype(s).
- adds the ability to read "table" format pandas hdf5 files in the coadd reader.

This release adds the truth catalog and its reader. It also uses GCR 0.7.2 which has some new user-friendly features.

This is an alpha release of `GCRCatalogs` v0.8.0. We plan to release v0.8.0 in about a week, for the CMU Collaboration Meeting.

There have been many updates since v0.7.x. Most notably, there are readers for DC2 Coadd Catalogs, DC2 Reference Catalogs, DC2 Instance Catalogs, and also focal planes. A full change list can be found [here](https://github.com/LSSTDESC/gcr-catalogs/compare/v0.7.8...v0.8.0-alpha).

Update to latest version.