Icons: process_icons(), create files only if icons_dir is set
Func 'match'/Types: add global_data variable
global_data: make available to eval functions (compiling, test)
Icons: Get dimensions of icons and make available as global_data
Stat: add possible values from @postprocess
Stat: @postprocess: simulate statement, so that prop() gets evaluated
global_data: first evaluate all properties, then compile global_data
Func 'check': compile @depend_properties in order as they appear
Property text-offset: if not set, calculate from icon/symbol size (below)
Prop text-offset: Bugfix, global_data might not have 'icon-image'
New property: text-anchor-vertical (below, above)
New property: text-anchor-horizontal (left, middle, right)
Merge pull request #38 from plepe/text-offset

Calculate text-offset from icon/symbol size; introduce text-anchor-vertical and text-anchor-horizontal