Rename components of the Matrix object

There were simply too many "m"'s floating around so rename the
components of the Matrix structure to 'c'.
Matrix: use std::swap instead of own function
Util: inline utility functions
docs: a remark on C++11 and clang
UnitTest: a basic unittest framework
tests: add a few simple tests

A few tests to check the basic properties of the Matrix, Point and
Vector classes. This also demonstrates the usage of the test framework.