Merge pull request #19 from ukolka/master

Created add_parent method and fixed few typos in doc strings.
Removed defaulting asignee for task to me. Now asignee is completely optional. If not given, then a task has no asignee
Merge pull request #21 from jaredlwong/create_task

Removed defaulting assignee for task to me.
Merge pull request #20 from ukolka/master

Added create_subtask method
Bug & pep8 fix, version bump

- Fixes #17
- Few pep8 fixes
- Bump version since some new calls where added
added AsanaAPI.rm_tag_task and AsanaAPI.get_task_tags
Merge branch 'master' of github.com:ukolka/asana