zshrc: set histignorespace.

This option prevents items from being in the history if they start with
a space.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
vimrc: highlight vim help as "help", not "asciidoc".

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
vimrc: don't highlight whitespace issues in help.

There's nothing we can do to fix it, so don't bother complaining about
it.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>