Update the file parser to support blank lines.

The blank lines are submitted as notes with a value of -2.
Songs no longer play invalid notes.

Songs will now skip invalid notes.
Invalid notes are notes with values not within the -1 to 1 range.
Added necessary NOT operator.

lolwoopsy
Fixed using wrong field names.
Merge pull request #1 from Ijwu/master

Added ability to place rests in the files.