Better descriptions

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`
