Closes #363

By an unhappy accident, OTP21 added functionality for 'named' trace
functions. This has a pattern match that matches the old trace function
(a 2 tuple where the second element is itself a 2 tuple):

https://github.com/erlang/otp/pull/1781

This patch changes to using a versioned record (so we can extend the
tracing later if needed) and adds 3 more options to tracing; count,
timeout and format string.

Additionally, tracing an OTP process via start_link arguments is now
documented.

According to the official changelog for elixir 1.5 parse_transform is
deprecated since this version. See
https://github.com/elixir-lang/elixir/blob/v1.5/CHANGELOG.md#4-deprecations

Emphasize application variable

* A side effect is you can set per processes functions via lager:md/1

* Updated README with instructions on how to use
 * Basic set of tests for working and non working examples