Compiler/Stat: convert structure to class
Compiler/Stat: change calls to new class interface
Compiler/Stat: remove old legacy interface
Merge branch 'master' into stat-as-class

Conflicts:
	pgmapcss/compiler/stat.py
	pgmapcss/main.py
	pgmapcss/mapnik/process_mapnik.py
	pgmapcss/eval/eval_is_prop_set.py
Merge pull request #43 from plepe/stat-as-class

Stat as class