Several changes to zpar.lib.cpp

- Added `parse_tagged_sentence()` and `dep_parse_tagged_sentence()` to allow parsing of already tagged sentences.
- Removed `format_tagged_vector()` to write out properly formatted tagged sentences since that functionality is already provided by `CSentenceWriter` in Zpar.
- Similarity, used `CSentenceWriter` to write out properly formatted tagged sentences to the output file in `tag_file()`
- Fixed several comments in the code.
Putting `format_tagged_vector()` back in since CSentenceWriter cannot write to streams, only files.
Adding simple unit tests.
Merge pull request #11 from EducationalTestingService/feature/add_unit_tests

Unit Tests
Merge branch 'develop' into feature/parse_tagged_sent
Added `parse_tagged_file()` and `dep_parse_tagged_file()` function to parse pre-tagged files.
Added pre-tagged data file.
Expose `parse_tagged_sentence()` and `parse_tagged_file()` on the python side.
Added new tests for parsing tagged sentence and file.
Added methods to dependency parse tagged sentence and file.
Added new tests for dependency parsing of tagged sentences and file.
Added .gitignore
Update the README and `zpar_example.py`

- Include an example of parsing an already tagged sentence.
Merge pull request #12 from EducationalTestingService/feature/parse_tagged_sent

Added function to parse already tagged sentences and files.
Updating version numbers.
Merge pull request #13 from EducationalTestingService/develop

Adding simple unit tests and new function to parse already tagged sentences and files.