Allow [skip appveyor] and co in commit body

 
Hi All,

As Ben recently pointed out, appveyor only honours [skip xxx] messages
if they are in the commit title.  The article Ben linked to (a couple
of times removed) has a script that gets appveyor to also honour the
messages if they are part of the commit message.  I've made a PR with
the relevant change:

https://github.com/OpenSmalltalk/opensmalltalk-vm/pull/349

The drawback of this is that in some cases when merging multiple
commits the skip message may be left in and the build accidentally
skipped.  I don't think this has been an issue for us, and we can
always back this change out.

What do you think?

Cheers,
Alistair