fix issue #215: lager.app env overwrites default handlers

the default handlers defined at lager.app overwrites handlers defined previously by application:set_env(lager, handlers, ...) if lager application is started application:start(lager)
Merge pull request #216 from fogfish/master

fix issue #215: lager.app env overwrites default handlers
lager_backend for use with common_test
@doc for lager_common_test_backend
Removed 1.X support
cleaned up lager_common_test_backend:bounce for log level
Merge pull request #224 from joedevivo/master

lager_common_test_backend
Fix line numbers detection in tests for OTP >= 17
Fix ct backend dialyzer warnings

* Fix unmatched return
* Fix set_loglevel call to store mask in state
* Add common_test to plt for ct:pal spec
Add maps formatting

Note that compiling on OTP 17.0, or later, will produce beam files
(specifically lager_trunc_io) that are incompatible with R16B03-1, or
earlier, due to erlang:is_map/1 using a new beam opcode (156). However
if compiled on R16B03-1, or earlier, will produce beams files that are
compatible with 17.0, and later, and maps will be formatted where
supported by the active OTP release.
Update tools.mk
Merge pull request #237 from fishcakez/ct_backend_dialyzer

Fix ct backend dialyzer warnings
Merge pull request #236 from fishcakez/maps

Add maps support
Merge remote-tracking branch 'upstream/master'