transformers-compat-0.7.2: A small compatibility shim for the transformers library

This package includes backported versions of types that were added to transformers in transformers 0.3, 0.4, and 0.5 for users who need strict transformers 0.2 or 0.3 compatibility to run on old versions of the platform, but also need those types.

Those users should be able to just depend on transformers >= 0.2 and transformers-compat >= 0.3.

Note: missing methods are not supplied, but this at least permits the types to be used.