allow including a detailed log in refchange emails

This can be a good intermediate between emails about individual new
commits (may be annoying for people who do not want to receive too many emails)
and the one-line summary included by default in the refchange summary emails.
Split diffOpts and logOpts settings using shlex.split().

The two options diffOpts and logOpts are command-line options.
Splitting them into words on whitespace was too crude, because
individual command-line options might need to include spaces; e.g.,

    git config multimailhook.logopts '--pretty=format:"%h %aN <%aE>%n%s%n%n%b%n"'

So instead use shlex.split(), which understands quoting etc.

With help from: Matthieu Moy <Matthieu.Moy@imag.fr>
Merge branch 'refchange-showlog'

* Allow including a detailed log in refchange emails.

* Parse multimailhook.{diffOpts,logOpts} using Python's shlex module.

Conflicts:
	git-multimail/git_multimail.py