Scour

* Fix bug when removing stroke styles
* Remove gradients that are only referenced by one other gradient
* Added option to prevent group collapsing
* Prevent groups with title/desc children from being collapsed
* Remove stroke="none"

* Remove unnecessary nested `<g>` elements
* Remove duplicate gradient stops (same offset, stop-color, stop-opacity)
* Always keep fonts inside `<defs>`, always keep ids on fonts
* made ID stripping optional (disabled by default)

* moved all functionality into a module level function named 'scour' and began adding unit tests
* prevent metadata from being removed if they contain only text nodes
* Remove unreferenced pattern and gradient elements outside of defs
* Removal of extra whitespace, pretty printing of XML

* Prevent error when stroke-width property value has a unit
* Convert width/height into a viewBox where possible
* Convert all referenced rasters into base64 encoded URLs if the files can be found

* Removes unreferenced elements in a `<defs>`
* Removes all inkscape, sodipodi, adobe elements
* Removes all inkscape, sodipodi, adobe attributes
* Remove all unused namespace declarations on the document element
* Removes any empty `<defs>`, `<metadata>`, or `<g>` elements
* Style fix-ups:
* Fixes any style properties like this: `style="fill: url(linearGradient1000) rgb(0, 0, 0);"`
* Removes any style property of: `opacity: 1;`
* Removes any stroke properties when `stroke=none` or `stroke-opacity=0` or `stroke-width=0`
* Removes any fill properties when `fill=none` or `fill-opacity=0`
* Removes all fill/stroke properties when `opacity=0`
* Removes any `stop-opacity: 1`
* Removes any `fill-opacity: 1`
* Removes any `stroke-opacity: 1`
* Convert style properties into SVG attributes