Fix question marks at the start of commit messages.

When committing the plugin forces Mercurial to use UTF-8 encoding for
messages, however, it wasn't forcing Mercurial to use UTF-8 encoding
when retrieving commit messages from "hg log". On Windows the
encoding defaults to the current system codepage, not UTF-8, so the
messages weren't decoded correctly. This fixes #6.
Unescape XML entities in commit messages when retrieving file history.

This fixes #5.