Start work on label rendering
start label styles and positioning
mostly working path and point labelling
Add rtree to index.html
Merge branch 'master' into labels

Conflicts:
	js/id/renderer/map.js
	js/id/svg/lines.js
Merge remote-tracking branch 'systemed/master' into labels

Conflicts:
	js/id/svg/lines.js
	js/id/svg/surface.js
Add polygonCentroid and polygon area to utils
add very basic support for area labels
Add rtree.js
start rearranging label code
Split up pathTransform
Add pathLength to utils
Add label_stack
Try multiple line label positions
Add classes to labels for styling
Merge remote-tracking branch 'systemed/master' into labels

Conflicts:
	js/id/renderer/map.js
Labels height pulled from font-size css
Point halos and test width calculation/estimation
Halos and proper orientation for line labels
Label bugfixes and cleanup