Update README.md now that Nucleus does support python 3.8.

Update README.md

Automated g4 rollback of changelist 392771263

Temporarily fix the TF version at 2.5.0 to deal with e2e test failures.

Resolve String Error Code Usages

Upgrade Nucleus to support TF 2.6.0.

Fix a string constant that was breaking the build.

Update Nucleus to allow (optionally) keeping only the specified auxiliary tags.

Add an variable in build_clif.sh so that we can optionally pin CLIF version as needed.

Get Nucleus to build on Ubuntu20.04, with Python3.8.

Don't depend on Tensorflow's error code string representation in tests,

Add Beam readers for BED and SAM/BAM files.

Uninstall older libclang so that that cmake finds the newest one.

Update documentation.

Upgrade Nucleus to support TF 2.5.0.