Add export support for DrawView

Export the current drawing as either a BezierPath or UIImage
Exporting and Archive loading fixes

Fixed bug with BezierPath representation of drawing view. Updated
example code to read newer archived path data.
Removed old test path data
Updated CocoaPod version and Readme
Added support for modes.

Added mode support with UI for user signatures.
Updated readme with a signature mode example.
Added ability to clear drawing.
Updated CocoaPod Changelog
Changed stroke color to property.

Removed backgroundColor property since the UIView has a background
color property already.
Added stroke width property.
Merge branch 'wip-1.0.0'