Updated agenda

* Switched to using 't' for changing todo state rather than 'c'
* Cursor position fix to keep cursor in the same line upon refresh
Updated agenda, parser & time

* Refactored parser & time to reuse functions rather than create
  anonymous funtions which can lead to heavy memory consumption.
* Refactored & Updated agenda & parser to allow for serialization and
  saving of files back to file system.
* Added more Agenda view apis for manipulation of headlines.