- bring CSS lexer to the CSS2.1 spec (http://www.w3.org/TR/CSS2/syndata.html)
- CSS override rules are broken. For example, text-offset-y and text-offset
  should override each other, but currently they are mixed upon rendering.
  Does it matter?
- Fixing of label positions should include some margin
- Clean up shp.c

* Merge changes from poskole2015 branch (waits for merge of automatic labelling):

  - icon-offset-{x,y} (commit c766658cd89232da2238aceeebcd4b3cc1b1a8c8)
  - (major-)z-index-fixup (commit 65930752a89084c4f17440a9fdc5548801134638)
  - casing-z-index (commit 65ad3116fc4ff85fdf8c2945f37d1d97cfe86c34)