Added instructions on how to run PCA on GCE
Merge pull request #48 from elmer-garduno/master

Added instructions on how to run PCA on GCE
Updated README run PCA documentation.
Merge pull request #51 from elmer-garduno/update_readme_run_pca

Updated README run PCA documentation.
Upgraded to v1beta2
Merge pull request #52 from elmer-garduno/upgrade_to_v1beta2

Upgraded to v1beta2
Added FixedBasesPerReference as the default split for VariantsPca

Renamed split methods, added documentation and unit tests.
Added request, variant and reference span counters.
Merge pull request #49 from elmer-garduno/master

Added a fixed bases per reference splitter.