First step: make usage to textMeasure only take in text selections
643 - TextMeasurer takes in a temporary text node to measure against
Aligning usage to be in line with new getTextMeasure

Now measurers need only be created once and can be reused
Updating jsdoc on getTextMeasure
getTextMeasure -> getTextMeasurer
Minor format fix
Merge branch 'master' into 643-improveTextMeasurer

Conflicts:
	plottable.js
	src/components/categoryAxis.ts
	src/components/numericAxis.ts
	src/components/timeAxis.ts
Merge branch 'master' into 643-improveTextMeasurer

Conflicts:
	plottable.d.ts
	plottable.js
Merge pull request #807 from palantir/643-improveTextMeasurer

643 - improve text measurer