Add missing entries for '7sus4', 'add11', 'add13', 'add9' to chord_shorthand

[yaph]

A call like from_shorthand('C7sus4') resulted in an "Unknown shorthand" error. I noticed that some other entries in chord_shorthand_meaning were not present in chord_shorthand so I added these as well.

To run make test I had to install numpy.

The following call still results in an error, but I don't know the code well enough to make it work:

from_shorthand('C9b5')

[BonifacioCalindoro]

Nice work

[ldrolez]

I think 11 and add11 are different: add11 has an added 11th without the 7th and 9th Same problem with add13

[BonifacioCalindoro]

I think 11 and add11 are different: add11 has an added 11th without the 7th and 9th Same problem with add13

Exactly, those chords imply different notes. That difference is necessary for the robustness of modern harmony