Upgrade to lager 2.0.1

This allows us to use lager's tracing again without fear. The fix is in
basho/lager#175.
Add lager_syslog dependency for optional syslog loggin
Update release notes for 1.4.3
Merge branch 'feature/upgrade-lager-to-2.0.1' into release/1.4
Merge branch 'feature/1.4.3-release-notes' into release/1.4
Merge branch 'release/1.4'