FIX clean shutdown in supervision tree
Correctly shutdown the worker supervisor

Closes #53.
Bump version to 1.2.2
Update README
Update .travis.yml
Merge branch 'clean_shutdown' of github.com:quiquepaz/poolboy into quiquepaz-clean_shutdown

Conflicts:
	src/poolboy.erl
Bump version to 1.3.0
Update README.md
allow pids in typespecs
Merge pull request #57 from sasa1977/fix/typespec

allow pids in typespecs
Fix setting monitors on calling processes
When process was in the waiting list it was monitored twice and only one monitor
was canceled.
Merge pull request #58 from ppikula/fix_monitors

Fix setting monitors on calling processes
Add 17.3 to .travis.yml
Use erlang.mk
Merge github.com:devinus/poolboy