Refactoring/cleanup

- Factor out common behavior for reader/writer classes
- Remove BED, VCF classes for now.  Need to be rethought offline.

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122065]
Streamline documentation start page

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122212]
Start documenting BasH5Reader

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122213]
Better README

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122222]