add changelog style to command line template.
to use, "hg log --style=changelog". makes different output with no
flags, -q, -v, --debug.
templater module has new template filters for this.
email - committer email address
fill68 - refill text to 68 colums
fill76 - refill text to 76 colums
tabindent - prefix every not empty line with tab
shortdate - iso 8631 date, no time zone
stringify - turn template iterator into string