templatekw: clean up implementation & test; add help. The core logic is cleaned up and moved to the wrappers module. The test made to test that it works with original Mercurial changesets, is cleaned up so that it can be more easily extended in the future. Finally, documentation is added for the feature.

97f2079e3778511944ffb6a662520580650a3993 1.0
09c016174e332eceda015d3f43d96d7e0228acf3 1.0.1
4359ddd73b009fbb356c52ea5d99cba25222ee7a 1.1
8e621dbb82d4363a85317638ad237e2817c56347 1.1.1
093ae2915b452539b44390ee4ea14987484e1eee 1.1.2