Correct y position for 'inline' articulations

Staccato, Staccatissimo, Accent, and Tenuto are drawn between stave lines when appropriate, and they will avoid overlapping any lines.

Tweaked placement of some articulations so that they don't overlap when stacked on the same note.

There is still room for improvement in the drawing functionality when dealing with multiple articulations on a single StaveNote. Instead of keeping track of a single 'line_spacing', you could keep track of 'line_spacing_above' and 'line_spacing_below'. There is also still unwanted space between inline (i.e. staccato, staccatissimo, accent, tenuto) and non-inline articulations when they are all above the same Middle-C note.

New Functions:
* Vex.Flow.StaveNote.prototype.getLineNum(is_top_note)

New Tests:
* Articulation - Inline/Multiple (Canvas)
* Articulation - Inline/Multiple (Raphael)
![Articulation - Inline:Multiple](https://f.cloud.github.com/assets/134487/316674/4d4fa66a-9835-11e2-9c3c-01b67ac29747.png)