Added another suggested way to use cdiff with git

Diff of diff

Trying an older version

Common error of using lstrip:

 lstrip('\x00+') will eat all '+' after '\x00'

People complains lightgreen is nearly unreadable in solarized dark color
scheme.  Use green instead, which looks good enough for both

Use correct integer division

Without this, we get the following on Python 3:

    return '%s%*s' % (markup_fn(text), pad_len, '')
    TypeError: * wants int

WTF? docutils does not set up dependency correctly?  Or pip does not
handle it??

Python 3.4

Python 2.5 is not listed as supported version, according to
http://about.travis-ci.org/docs/user/languages/python/

Respect the `LESS' environment variable.

Steal a few more lines from git's pager code and only pass the hardcoded
"-FRSX" flags if the user has not set the LESS environmen variable to some
other variable, thus behaving more closely to what the user would expect.