fix: midnight theme — softer grid lines, subtler fill

feat: smart y-axis ticks with nice round numbers

fix: CSS variables cascade from theme wrapper to SVG

docs: add Why section to README

feat: move all styling to CSS, add Tufte/Midnight/Warmth themes

feat: add update(), destroy(), idempotent rendering, SVG element target

feat: v2 — zero-dependency rewrite with native SVG

Merge pull request #4 from benaskins/fix/issues-2-3

fix: correct drawPoints default in README and y-axis labels with lowerBound

Stylistic changes, remove disclaimer.

Missing from last commit.

Upgrade to latest raphael

Remove hover from swellchart example

Cater for negative values & tweak some of the examples.

Some custom graph experiments I've been sitting on.