README: Fix name of environment variable for debugging
Merge pull request #71 from PaulPrice/readme_debug

README: Fix name of environment variable for debugging
Log version, and output when requested.

Introducing the use of the ArgumentParser to handle the argument parsing.
This should not get in the way of any communication from git, because the
manpage for git-remote-helpers says:

SYNOPSIS
       git remote-<transport> <repository> [<URL>]

i.e., there are no -- or - options provided, so as long as all additional
arguments (e.g., --version) are prepended with hyphens, there's no worry,
and we can just dump all the other arguments into the HGRemote.
Convert ArgumentParser to OptionParser to support python 2.6
Merge pull request #70 from PaulPrice/version

Can't get version