correct string/number conversion in toBeWithinDelta
custom svg path matcher
use svg path matcher for line chart spec
consolidate custom jasmine matchers in helpers/custom_matchers.js
use path matcher everywhere.

down to one failure for #509!
refactor toBeWithDelta and toMatchPath matchers to allow reuse

as boolean predicates...  not something jasmine excels at (oh well)
use path matcher to check selection

because ie uses float precision and its own (standard but different)
path represention

closes #509