Changed how options are handled

- changed mgStyle to mgOpts
- options are stored as linked list
- removed tag from MGstyle
Tweaked layout calculations

- renamed mgRelative to mgPosition and mgPropPosition
- use x/y, width/height for prop and regular
- added content size
- tweaked when padding is applied
- renamed style.relative to style.anchor
Updated NanoVG, added paragraph, fixed Fontstash bug

- updated nanovg to latest
- fixed sub string bug in fonsTextIterNext()
- added support for text paragraphs, reflowing layout
- added line height support for text
Icon rendering, layout pack.

- added icon rendering using nanosvg and nanovg
- fixed overly eager tesselation in nanovg
- added pack param for layouter, aligns widgets along main axis when no
item is set to grow
- added icon button
- added icons from Entypo