Tablature engraving module

Upload and display tablature in the MEI or MusicXML file format.
Set up template transcription function

Polyphonic transcription module now calls a template function, in which
developers can insert their polyphonic transcription algorithm.
Detach darwintab modules

Robotaba should have its own copy of the guitar and note modules and
should not import from darwintab.
Transcribe display update

Moved display module and forgot to update the url redirect link. fixed.
Tabulate module call algorithm

Make tabulate module call template function, in which the user defines
their algorithm.
Algorithm template functions

Created template functions for the polyphonic transcription and guitar
tablature arrangement algorithms. All developers have to do is to insert
the algorithm into this function and return the contents of their
generated mei file as a string.

Fixes #14
MIT License

add MIT license header to each file. Fixes #13