Add/update file copyright headers where deterministically appropriate.

Note:
Many updates to rebar.config files have been scripted to ensure
consistency and likely have re-ordered configuration settings and options.
While the file may look significantly different, the content other than
dependency updates (and, in some cases, more stringent compilation options)
should be the same from rebar's perspective.

Sometimes there are a LOT of records going through logging backends
which contain notable number of empty (i.e. undefined) fields. This
humble patch solemnly introduces new function `lager:pr/3` designed to
help cope with such kind of issues, providing a one and only option `compress`
which, when turned on, effectively eliminates any empty fields in records.

Finish lager API modifications
Update config API to handle multiple sinks
Identify areas where new code is yet to be written

First pass at adding sink parameter into the external API layer.

TODO:
* config updates
* loglevel changes per sink