Some more .gitignore cleanup

Hide more of the files that clutter our directories

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Update documentation to remove SDE unpacking section

Our documentation explained in detail how to unpack Suunto DM export
files. This is no longer necessary as we now unzip them while opening
them.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>