More robust way of echoing $PATH

When we start a login shell to find the natural value of $PATH, instead
of executing `env` in that shell then grepping for $PATH, we simply
`printf` the $PATH directly.

This should be more robust (by virtue printing the value directly rather
than indirectly with env and then using a grep search for the answer.)
Set $TERM, $CLICOLOR, $SUBLIME vars in subshell

If your .bash_profile script does special stuff that may not be friendly
to executing in a subshell under Sublime (for example, echoing ANSI
control characters or the like,) adding a `if [[ $SUBLIME == 1 ]];
then... fi` block around those commands should help alleviate that.

We also set $TERM to 'ansi' so that we get the most basic, ANSI-standard
terminal output we can; and $CLICOLOR to an empty string ("") to turn
off ANSI color codes in the subshell.
Strip ANSI control chars from output. Fixes #3.

This plugin runs a login subshell and echoes $PATH from within it to
find the natual value of $PATH. However, as described in #3, some users
automatically print characters which mess with our parsing of the $PATH,
namely ANSI control characters.

This commit explicitly strips ANSI control characters from the output of
our `printf "$PATH"` command, using a regular expression in Python. The
regular expression in question was taken from
http://www.commandlinefu.com/commands/view/3584/remove-color-codes-special-characters-with-sed
.
Don't run if OS isn't Mac OS X (fixes #5)

We add an explicit check before loading the plugin to make sure the
current operating system is Mac OS X. If this check fails, none of the
plugin code is run (and thus, the path isn't touched) and a message is
printed to the Sublime console (View -> Show Console).

This will prevent this plugin from corrupting the path on Windows and
Linux as described in #5. As should be obvious from the plugin name and
README, this plugin is only designed to work on Mac OS X.