proxy: provide a simple proxy "redirecting" to HTTPS

This is not useful at all currently (unless you have a browser which
isn't able to do TLS). Next step is to make this proxy present a client
certificate (embedded browsers not able to do that are more common).
proxy: move to a dedicated directory and provide a Makefile

No vendorization of dependencies yet, but try to workaround the GOPATH
mess. No need for the user to setup a GOPATH. If a user want absolutely
to use its own GOPATH, they need to override the makefile one. Something
like:

    make GOPATH=${GOPATH}
proxy: don't remove GOPATH

In case it is overriden, a user wouldn't be happy with that.
proxy: minimal proxy

We just do a regular proxy.
proxy: add an option to log to syslog as well
proxy: switch to op/go-logging for logging

This one seems to work reasonably well.
proxy: move configuration file parsing into dk/config
proxy: start some tests
proxy: provide a sample configuration file with default values
proxy: ability to merge configuration items and URL pattern matching
proxy: remove dk.test when tests are done
proxy: build in `build~`

It gets ignored by default by most people.
proxy: implement X-Frame-Options stripping
proxy: move into `contrib/` directory
proxy: correctly parse glob operators

Transform a glob pattern into a regular expression. We cannot use the
`Match()` function in `filepath` because it assumes the use of filenames
and `/` is special.
proxy: add an option for appending X-Forwarded-For
proxy: add X-Forwarded-For to the request, not the response
proxy: handle cases where we don't get an answer

This happen for example when we are unable to establish a TCP session
with the target.
proxy: add an option to do request over HTTPS
proxy: handle reverse proxy path when redirecting to HTTPS

When the answer contains a `Location` header, we modify it to use
`http://` instead of `https://` if the resulting URL would have been
queried over HTTPS.