Fix order of operations in Pitch.difference()

Order of subtraction reversed to return the correct value.
added duration method
fixed issue1
fixed the duration issue (#5)
changes
zz
Merge pull request #13 from anishathalye/patch-issue-6

Fix order of operations in Pitch.difference()
Merge pull request #14 from shaladi/master

[bug-fix] changed octave to 12 semitones (from 16)
Merge pull request #15 from sudotong/master

Fixed issue #4
Merge pull request #17 from huase/master

fixed the duration issue (#5)
Merge pull request #18 from aaronzwiebach/master

Added Exception
Merge pull request #19 from nconsul/master

fixed issue1
Merge pull request #20 from Zulzaga/master

Fixed issue #7.
fixed the checkRep method of concat
Fix typo
Update Note.java

Should be false if obj == null‼
Merge pull request #21 from anishathalye/patch-issue-12

Fix typo
Merge pull request #22 from yongyi781/master

Update Note.java
Merge pull request #23 from sudotong/master

fixed issue 9--implementing checkRep of conca
Merge pull request #24 from shaladi/master

[feature] Concat now has a getter 'second' for the second piece of music