Vim: tweak JSDoc snippets

I thought that it would be nicer to use "pa" as a trigger for `@param`,
but it didn't take, so I am changing it back.

I also wanted to remove a tabstop and some unnecessary filler text from
the snippets to make them faster to use.
Overcommit: exclude .gitconfig check for HardTabs

Git uses hard tabs when it manages .gitconfig files, so I don't want to
blow up when I modify this file because it has hard tabs.
Git: remove whitespace fix

This setting makes checking in third-party code, such as that added by
npm or bower, a chore because it strips trailing whitespace when
committing but leaves it in the working tree. Since I am using
overcommit to guard against whitespace problems where I care about them,
I don't really get much value out of this option and am removing it.
Vim: add some YARD snippets

I occasionally venture into the Ruby side of things where we are using
YARD for inline documentation. This commit adds a couple of snippets
that will help me write YARD a little faster.
Vim: disable syntastic when running :Acks

I have :Acks set up to make multi-file find/replace a little more
comfortable in Vim. However, it was running slowly because syntastic was
running after saving each file. Since I am not actually opening the
files and looking at them, I wasn't getting any value out of this and
want to just disable it.

I originally looked for a command that explicitly disables it instead of
toggling it, since the original state could be off (which would turn it
on for the :Acks run), but that doesn't seem to exist so I am just going
to run with :SyntasticToggleMode for now and see if I run into any
issues. Since I am not usually turning it off, I don't expect to run
into any.