Generalize language for pagination
Generalize language for pagination

Previously the section was very strict in what pagination was, however this isn't the reality for the matrix specification. Several endpoints have their own pagination naming conventions and do not follow those mandated by this section.

This commit generalizes the language to cover those endpoints while also describing how pagination works. In particular, it describes the rough API shape to expect and how to deal with the responses.

This commit also removes the `M_BAD_PAGINATION` error as it is not used in the real world. Homeservers are instead encouraged to use the standard `M_INVALID_PARAM` or similar error code.

Fixes https://github.com/matrix-org/matrix-doc/issues/610
Fixes https://github.com/matrix-org/matrix-doc/issues/1523
matrix-org/matrix-doc,matrix-org/matrix-doc,matrix-org/matrix-doc,matrix-org/matrix-doc