Initial / retained context values, bug fixes, image smoothing quality

#125

• Fix measureText / getTextSize following TypeScript upgrade (in v0.7.0) backported to 0.7.3
• Add setImageSmoothingQuality and getImageSmoothingQuality
• Set initial canvas values upon construction (for cross-browser consistency)
• Restore canvas context values when resizing the element (including clearing the canvas)
• Update docs examples
• Improve density in examples
• Fix redrawing bug in IE multi-line text example (by calling beginPath before drawing lines)
• Add module entry to package.json