Export ReaderBase, WriterBase classes from pbcore.io

[Tracking bug 23893]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 127983]
Cope with trailing ; in GFF attributes

[Tracking bug 23893]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 128030]
Whitespace

[Tracking bug 23893]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 128031]
Bug 22415. Fix pbcore doctests.

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 128121]
Bug 22415. Autopep8 pbcore.deprecated.ReferenceEntry.

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 128122]
Bug 23925
Merge to mainline to resolve repository metadata

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 128167]
Bug 23925
Delete file again after integrate

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 128168]