Create Orchard Core APIs Documentation

[hishamco]

It would be useful if we can add api.orchardcore.net something similar to .NET APIs docs

[Piedone]

This would need inline docs in the Orchard APIs which idea didn't really progress.

[hishamco]

We already did a progress in the past and most of the newly added APIs are documented. May be we need sometime to revise and add the missing docs