Implemented Storage class
Added exception for Storage and more tests
Fixed indents
Merge branch 'master' into storage_impl

Conflicts:
	deltacompression/storage.py
	deltacompression/storage_test.py
Added dot to comment
Merge branch 'master' into storage_impl

Conflicts:
	deltacompression/storage.py
Merge pull request #6 from zpp-2014-15/storage_impl

Implemented Storage