switch to lager, untested
use ?LEVEL instead of ?LEVEL_LOG
fix: return value on gen_server:call/2

to prevent crash of caller
Merge branch 'switch_to_lager' of https://github.com/paulperegud/erltweet_stream into paulperegud-switch_to_lager

Conflicts:
	src/erltweet_stream.erl
Merge branch 'paulperegud-switch_to_lager'