RtReadme is just one class which implements Content.
Content will be implemented by class that represent file/dir content.
It is based on different request path. 
And it requires different parameters : path and ref .
RtReadme requires two CTORS : for default branch and for branch referenced by "ref".
The same is true for RtContent for "file/dir". As a result there will be ambiguous  CTORS with the same number of parameters and same types but different semantics. I can introduce boolean parameter but it looks ugly.