Git: ksdiff-fixed uses absolute paths, lowers sleep timeout

the ksdiff-fixed script is a wrapper around ksdiff (Kaleidoscope.app's
command-line launcher) which fixes a bug where it would cause git/bash
crashes if its launch environment wasn't just so.

This commit updates the script to use the absolute path to the main
`ksdiff` command. In this way, it will successfully launch ksdiff no
matter the current $PATH (useful specifically when launched from GUI
apps, which use a different $PATH than Terminal apps.)

This commit also opens Kaleidoscope by bundle ID, rather than app name,
which should be a little more robust. It also doesn't open Kaleidoscope
in the background, making it seem more responsive.

This commit also has a lower `sleep` value after launching Kaleidoscope,
which makes it even more responsive without seemingly causing any
problems.

Finally, it updates the comments to be clearer.
Git: fix Kaleidoscope crashes from SourceTree

The same crashing bug we were seeing before when launching
Kaleidoscope.app from the terminal via 'git' also affects SourceTree. We
can use the same ksdiff-fixed wrapper script to fix this.

This commit updates the config in ~/.gitconfig to change SourceTree's
diff and merge tool to be ksdiff-fixed, rather than plain ksdiff.
Git: change "conflictstyle" to 'diff3'

No idea what this does, but people say we should do this, so OK?
Vim: remove 'w', add 'a', to formatoptions

'w' added trailing whitespace to wrapped lines to indicate they
continued on the next line, but this goes against the 'no trailing
whitespace' code/commit message formatting rules.

'a' automatically updates the formatting of paragraphs as we insert or
delete text.

We also change the `set` command to use "+=" and "-=" instead of a
straight "=". Vim's help recommends this to support additional format
options that are added in the future.
Homesick: add placeholder (noop) .homesickrc

This file can be run by homesick after symlinking a castle. It is a ruby
file, with the "this" variable set to the homesick object.

Right now, it just contains comments telling us future TODOs. Later we
can expand it to actually do these TODOs.
Git: change email to plain "github@" one
Merge commit '1b5318dfd5549f4d8068d591b3843b5915495e47'