Priorities, intrinsic size, fitting size & EVFL extensions

Core:

• Added support for priorities.
• Added support for z-indexing.
• Added ability to set the intrinsic width and height for sub-views.
• Added ability to get the fitting size of a View.
• View-names now have to follow strict C-identifier name rules (cannot start with a digit or contain '-').

Extended Visual Format:

• Added support for operators + and - (e.g. [view1(view2+100)]
• Added support for attributes accessors (e.g. |[view1(view1.height)]|
• Added support for line comments (e.g. |[view1]| // line comments)
• Added support for z-ordering (e.g. Z:|[view1][view2])