Support lager 2.0 data format
Merge pull request #1 from mururu/lager-2

Support lager 2.0 data format by @mururu. Thanks!
fluentd still uses old spec of msgpack: fixes #2
pin msgpack version
Fix rebar.config syntax error
Use msgpack old spec
Return standard 'ok'
Register fluent_event event in sup

Also avoids `undef` errors on app startup
Merge pull request #3 from climvalencia/master

Use msgpack old spec