Sacc

What's Changed
* Allow the concatenation of independent data sets with common tracers by carlosggarcia in https://github.com/LSSTDESC/sacc/pull/63
* Deprecated numpy alias by xgarrido in https://github.com/LSSTDESC/sacc/pull/65
* Added method to rename tracer (issue66) by carlosggarcia in https://github.com/LSSTDESC/sacc/pull/68
* Added method to remove tracer and the data associated (issue67) by carlosggarcia in https://github.com/LSSTDESC/sacc/pull/69

New Contributors
* xgarrido made their first contribution in https://github.com/LSSTDESC/sacc/pull/65

**Full Changelog**: https://github.com/LSSTDESC/sacc/compare/0.4.9...v0.5

Fixes a bug in keep_indices for block-diagonal covariances.

Fixes a bug when cutting out parts of a block-diagonal covariance.

- Fix performance on NERSC by buffering, at the cost of memory.

Fixes a bug with saving and loading bandpowers, and adds some better unit tests.

Fix error reading old files in last release.