Added debug output operator for Buffer::Target.
Math: properly test conversion constexpr also in Vector subclasses.
Math: test that implicit conversion of T to Vector<T> won't compile.

"Won't compile" tests are another awesome feature of C++11.
Math: test that implicit conversion of underlying type can't compile.
Math: test that implicit conversion from/to foreign types can't compile.
Math: updated Rectangle test to test constexpr functions.
Math: test that implicit conversion of Rectangle type can't compile.
Math: test that implicit conversion vector <-> complex/quat can't compile.
Math: test also possibility of Unit implicit conversions.
Platform: better way to specify application configuration.

Each implementation of *Application::Configuration will have different
methods tailored to feature set of the underlying toolkit. Currently
each windowed application's Configuration has only window title (except
NaClApplication) and window size. WindowlessGlxApplication has empty
class. More features will come later. Also created introductionary
documentation for Platform namespace.
Minor documentation fixes.
Merge branch 'master' into compatibility