Merge pull request #8 from sdboyer/master

Introduce Set interface & Each method
Add Sam Boyer to Credits
Merge pull request #9 from sdboyer/master

Idiomatic Go: use defer for mutex unlocks.
Update .travis.yml to use Go version 1.2
Merge pull request #11 from sdboyer/master

Introduce non-threadsafe Set implementation
Update README.md
Add intersection tests
Add a new "New" method to the Interface

This is needed mainly to create a new set from other methods where we do not have any knowledge about the underlying struct. Also this will be helpful for #13
Add New() for ts struct too
Forgot to add document
Write a more faster intersection method.
Fix package description
Catch up to addition of Set.New()

Conflicts:
	set_nots.go