Eval::differing: bugfix, call eval_metric with list of parameters
Eval::identical, equal, differing, nonidentical: bugfixes, more tests
Merge branch 'branch-0.6'
Change to version 0.7-dev
Include icons from https://github.com/mapbox/maki
Add 'id' to stat structure, don't pass to functions directly
Compile Function Check: Bugfix, pass indent as correct parameter to print_checks
Eval: pass 'stat' to compile_eval and to function compiler
Compile Eval: compile functions with no parameters with custom eval compiler
Eval-function: style_id()
Internal Function: to_int()
Eval: new function substr()
compiler::stat(): takes additional parameter value_type
Support for icons from Mapbox Maki project
icon-color: change color of icons (only for icons from Mapbox Maki)
icon-size: change size of icons (only for icons from Mapbox Maki) (sizes: 12, 18, 24)
compiler::stat: stat_property_values() takes add. parameter pseudo_element
compiler::stat: new func stat_properties_combinations()
compiler::stat: smart combinations of properties

- new fun stat_properties_combinations_smart()
- stat_properties_combinations() accept include_illegal_values, pseudo_element,
  value_type
compiler::stat: register functions for generated properties (e.g. final-casing-width)