Rename fix_string to fix_string_case and add tests for it

The name fix_string_case makes more sense since the function converts
case of characters in given string. Also, tests ensure that is
converts properly.
Fix documentation in test_utils_validate.py
Add tests for utils.count. Fix case transform in count functions

Also, edit test_utils_validate.py to add correct references in
documentation.
Update ChangeLog and make package version number more Pythonic

Other changes:

 - Bump up package version to 0.1.2
 - Fix function reference to fix_string in avro.py