resource(".xls") -> Excel

adds into(DataFrame, Excel) using pd.read_excel
Merge branch 'master' into resource_excel

Refactor resource(Excel) for new regex technique
add into(DataFrame, Excel) tests in test_into.py

Conflicts:
	blaze/api/into.py
	blaze/api/resource.py
	blaze/api/tests/test_resource.py
	blaze/data/__init__.py
Merge branch 'master' into resource_excel

Conflicts:
	blaze/api/tests/test_into.py
Merge pull request #539 from talumbau/resource_excel

resource(".xls") -> Excel