Add failing test for additive identity
Merge branch 'master' into additive-identity
Special case zero lines
Line count is off by one error
Merge branch 'master' into additive-identity

Conflicts:
	lib/source_map/map.rb
	test/test_map.rb
Add pipe identity test
Merge branch 'master' into additive-identity
Copy missing map over in pipe
Only care about piping one direction
Edge case pipe identity map
Merge pull request #4 from maccman/additive-identity

Preserve additive identity