Additional Box2D functions

[garrettrayj]

Currently PHP7 Mapnik only implements the bare minimum requirements for constructing Box2D objects. There's plenty of low hanging fruit in the C++ API that would make working with envelopes easier...

• width() and height()
• expand_to_include()
• contains()
• intersects()
• re_center()
• clip()
• pad()
• etc.

Should probably do a PHP implementation of the coord class before tackling this.

[africanrhino]

yeah, those are a great idea.