changed image tag to an anchor containing a red text "X". Turns red when hovering over it for some reason, but I like it so it stays for now.
added overlay canvas. Currently does nothing

Existing issues:
- no events associated with it yet
- causes floating Layer toolbar to appear behind it (not a big deal, going to be replaced anyway. If it isn't, just use an even higher Z-value).
- arbitrary z-value (currently a constant set at 100000. This is due to browser being unable to handle Number.MAX_INTEGER for some reason.
added rectangle_button.gif and an image tag to the controls. The image tag is going to act like the button until I find a more visually pleasing alternative. No functionality at this point.
added tool constants
added crappy rectangle button
removed commented blocks
added onClick event to rectangle tool button
Merge branch 'feature_rectangle_tool_UI_button' into feature_rectangle_tool
bounding box and drawing onto current canvas kind of work. Issues with over-writing existing strokes, and current values for stroke and fill not always working
draws rectangles to canvas. Can be turned on/off. Preserves line termination style.

ISSUES
-- causes lines drawn prior to a rectangle to try to form a polygon by joining start/end points. Then fills the interior.

-- drawing a rectangle over a scribble causes a weird effect where the scribble becomes a polygon and doesn't fill the same way as the rectangle. Does not draw over the scribble on same layer.
fixed glitches related to close/begin path. Shapes no longer fill when they shouldn't or merge with other shapes.
added ability to change fill color for shapes

TODO

-- change functions relating to stroke color to indicate this. Currently using "fill" to refer to "stroke" in several places. For now using "interior fill" to mean "fill"
fixed bug in IE that kept canvas from refreshing during rectangle boundary drawing. Need to begin and close paths before clearRect
ellipse tool added
fixed bug: adding layer resets fill style. Now preserves fill style. Same with clear layer
fill works, no button yet
added fill bucket tool
fixed bug introduced when drawing ellipses
added lock button
Still needs an active indicator
added red background indicator to lock icon when layer is locked
moved layer manipulation out to separate JS
moved fill and rectangle tools to own files
refactoring