doc: make paragraphs before example code end with "::" for reST syntax
This prevents lines in an example code from being treated as a part of
normal paragraph. For issue example, lines are folded into one
paragraph.
topic: centralize compatibility logic between hg versions into compat module
This patch can delay loading obsutil and obsolete modules until they
are actually used at "hg topics" or so, if demandimport of Mercurial
is enabled.