gendoc: guarantee that all commands were processed The new logic renders the commands belonging to each category in turn. Commands with an unregistered category are at risk of getting skipped because their category is not in the list. By comparing the list of all commands to a log of processed commands, we can detect commands with unregistered categories and fail with an error message. Differential Revision: https://phab.mercurial-scm.org/D6327

gendoc: group commands by category in man page and HTML help Make Mercurial's man page and HTML help group commands by category, and present the categories in a helpful order. `hg help` already does this; this patch uses the same metadata. This patch uses the same header level for command categories and for commands. A subsequent patch will push the command headers down one level. Differential Revision: https://phab.mercurial-scm.org/D6326

gendoc: indent loop to make next patch more legible Differential Revision: https://phab.mercurial-scm.org/D6325