added control for centering.
Added modifiers #, %, ! and *
Added an atom to track centering default value. Initial value is true.
Changed modifier to take a block, and create a union(){...}
Changed modifiers from !. to |.
Changed centering to centering!
Scale and Resize
Added import-file command.
Merge master into origin-import

Conflicts:
	src/scad_clj/model.clj
	src/scad_clj/scad.clj
Merge branch master into origin-Transformations
Merge branch master into origin-Center
Merge branch master into origin-mod
Merge pull request #18 from EricGebhart/Center

Center control for primitives.
Changed name to import.
Changed modifier prefix to -.
Merge pull request #20 from EricGebhart/import

Import-file
Removed my duplication of scale.
merge
Merge branch 'EricGebhart-mod'
Merge pull request #21 from EricGebhart/Transformations

Transformations, resize and scale.