Re-define now missing rebar.hrl logging macro's

As of this recent pull-request to rebar/rebar:
https://github.com/rebar/rebar/pull/281,
rebar/include/rebar.hrl no longer exists.

Since this project doesn't depend on any particular
version of rebar, and doesn't build with the
latest version from master, I have
reimplemented the logging macros that were previously
taken from the include file in the source itself.