use \w in LHS portion of regex
allow lines to begin with `export` keyword

* handy for re-using `.env` with shell scripts
* Foreman can load Pow-style `.powenv`
support YAML-like syntax

Key/value pairs can also be separated by `: `, allowing
for a YAML-like environment file. Among other uses, the
output of `heroku config` with the default format can
be used as an environment file instead of requiring that
`heroku config --shell` be used.
v0.2.0