Add object-attribute-writing-mechanism
Add test for attribute writing
Merge pull request #625 from matthiasbeyer/add-object_attr_writing_mechanism

Add object attribute writing
Add support for accessing booleans from objects
Add mapping from attribute to value-type
Added missing comments in object documentation
Add implementation for ws_value_set to string
Merge pull request #589 from matthiasbeyer/add-set_tostr

Add implementation for ws_value_set to string
Add attribute reading in buildin commands
Add builtin command for attribute writing of objects
Merge pull request #626 from matthiasbeyer/rewrite-abstract_shell_surface_attr_accessors

Refactor attribute accessors
Add zindex member for surface