Remove common style from composer class
Source class modification

* Remove piece and info attributes
* Insert title attribute
Function to get info from a cfg file
IMSLP info retrieval functions
Classes for Imslp info
IMSLP composer class and functions
Code improvements
Missing utils function
Fix left zero in imslp number string. Close #154

* There was no problem in IMSLP, but in my code.
Use IMSLP attribute name
Make complete score implementation (incomplete)

* There is no documentation
* The code doesn't import data from music21 stream
Move music21 functions to music module
Functions to get music basic information from music21 stream
Function tests implementation
Score object automation. Incomplete

* Song number and movement number are not yet implemented.
Fix IdCode parser
Fix song / movement problem. Solve part of #156
Fix sourceId retrieval. Solve part of #156
Small fix
Small code improvements