Simplify incremental API by removing Partial

Some can play the role of the Partial constructor as well, making the
latter redundant. By removing it we simplify the API and the
implementation.
Rename Some to Many to reflect its new behavior

Some suggests that there's at least one record returned, which is no
longer the case.
Update examples to follow changes to incremental API
Export HasHeader from Incremental and Streaming
Follow API changes in examples
Add .cabal file for examples