add BruteForce spatial partitioning strategy
changed unit testing structure
add submodules to collisions

- add two new submodules to collisions: detection and resolution
- moved collisions::broadphase to collisions::detection::broadphase
- new convention: all macros now end with a semicolon
add Contact struct

- new struct introduced: Contact
- renamed BroadPhase to Space, updated trait functions
new struct: ProximityPair

- introduced a new struct: ProximityPair
- updated BruteForce to use ProximityPair
- add missing documentation for ContactGraph and Contact
updated to latest Rust nightly build, support sphere-sphere collisions

- updated to latest Rust nightly build (2014-09-27)
- fixed compatibility issues
- add test cases for simple sphere-sphere collision tests