Fix significant performance regression on Firefox. #29

Fix alignment issues with RTL characters. #27

Fix glyph width for characters in RTL scripts. #26

• Added drawWithMetrics method that returns browser-provided TextMetrics for a glyph where available and trims SDF accordingly. #24
• Slightly improve performance #13
• Further cleanup of the code #18 #19 (h/t @mootari)

Fixed license id in package.json.