Better descriptions

[samanpwbb]

These parameters could use friendlier descriptions:
line-join
line-cap
*-gamma-method
*-simplify-algorithm
*-rasterizer
line-pattern-simplify-algorithm
text-placement
text-placement-type
text-placements
shield-placement
shield-placement-type
shield-placements

[springmeyer]

on my list to hit this.

[springmeyer]

Also need docs for raster-colorizer-*