decolorize: inital commit

Remove ANSI colour escapes from stdin.
.bash/shell: move xterm code up (no logic changes)
.bash/shell: use bright blue for HISTTIMEFORMAT
.bash/prompt: make PS4 useful for debugging

It occurred to me that you can use "dynamic" variables inside PS1 that are
not expanded until the prompt is displayed, and wondered whether you could
do the same with PS4. Turns out you can. This commit greatly enhances the
trace Bash gives you when you use "set -x" (or "bash -x"). It now shows
the name of the function and/or file, as well its line number.

I was having a lot of trouble with a shell script for a customer, and this
enabled me to find (and fix) the problem. Yay.

Of course, turns out other people have been using this same technique (in
different forms) for years:

http://raz.cx/blog/2005/08/handy-bash-debugging-trick.html
http://bashdb.sourceforge.net/bashdb.html#Interactive-Line-Tracing-Session
.bash/prompt: update PS{2,3,4} comments
git-tilde-log: tweak colours

On a non-customised terminal, black is pretty much unreadable, so use
dark blue.
git-tilde-log: make refs/branches stand out more

Before c7bf451, they used to be much more conspicuous. Now they are again, this
time in yellow.
.bash: only alias "ctags" if the command exists
.bash/commands: export LESS's defaults

This has at least two benefits:
* Scripts that execute "$PAGER" (including those quotes) now work. They did not
  before, because "less -BLA" (including the space) is not a binary on the
  system.
* I can simply do "some-command | less" instead of "some-command | $PAGER", the
  way root intended.

I do not know of any "less" implementations that do not support "$LESS".
.bash/shell: use en_US instead of en_GB

I prefer British English, but en_US is much more widely available. Because
the LC_* environment variables are passed on by default by "ssh", you would
often get "Cannot set locale" when connecting, even before the .bash_profile
from the server was processed.

Them Yanks done did win again, Joe.
git-tilde-log: use extended regex format for sed
git-tilde-log: also replace singular time units
git-tilde-log: use Perl, not sed

"sed -E" is not available in GNU sed, and Perl is on pretty much every system.
Now that I use extended regexes anyway, there is not really a point in staying
with sed.
.ackrc: add Twig to HTML and template file types
.bash/prompt: fix undefined variable in PS4

Discovered this while debugging a script that had "set -o nounset".
.inputrc: improve history-preserve-point comment
Added mamp and node stuff to the path (may remove)
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  .inputrc: improve history-preserve-point comment
  .bash/prompt: fix undefined variable in PS4
  .ackrc: add Twig to HTML and template file types
  git-tilde-log: use Perl, not sed
  git-tilde-log: also replace singular time units
  git-tilde-log: use extended regex format for sed
  .bash/shell: use en_US instead of en_GB
  .bash/commands: export LESS's defaults
  .bash: only alias "ctags" if the command exists
  git-tilde-log: make refs/branches stand out more
  git-tilde-log: tweak colours
  .bash/prompt: update PS{2,3,4} comments
  .bash/prompt: make PS4 useful for debugging
  .bash/shell: use bright blue for HISTTIMEFORMAT
  .bash/shell: move xterm code up (no logic changes)
  decolorize: inital commit