doc: show short description of each commands in generated documents Before this patch, short description of each commands is not shown in generated documents (HTML file and UNIX man page). This omitting may prevent users from understanding about commands. This patch show it as the 1st paragraph in the help section of each commands. This style is chosen because: - showing it as the section title in "command - short desc" style disallows referencing by "#command" in HTML file: in "en" locale, hyphen concatenated title is used as the section ID in HTML file for this style - showing it as the 1st paragraph in "command - short desc" style seems to be redundant: "command" appears also just before as the section title - showing it just after synopsis like "hg help command" seems not to be reasonable in UNIX man page This patch just writes short description ("d['desc'][0]") before "::", because it should be already "strip()"-ed in "get_desc()", or empty string for the command without description.