Doc changes, and two minor speed-ups

* Use low-level \if_int_compare:w rather than \int_compare:nNnF.
* Abuse \aftergroup to insert end-of-loop tokens rather than skipping
over them in a conditional branch at each iteration.
Add primargs test file for the read_token and read_x_token functions
Add a test that loading the package works out
Test that loading primargs and morewrites works, logging definitions
Add test files for getting a number/dimen/glue/mudimen/muglue
Mention the test primargs002 in primargs.dtx
Give morewrites.dtx the same version as primargs.dtx
Add copyright to a test file