Changelog for mcm-0.6.4.10

[0.6.4.10] 2016-06-28 - improve "mcm --help" output - fix why-can-immediate-locals-not-have-underscores bug - fix "let =" parsing oddity - slightly simplify compiled mcm output - spelling and punctuation fixes [0.6.4.9] 2016-06-25 - add one further parseerrortest - fix long-contents-with-some-$fragments-are-slow bug