Workaround Doxygen misparse.

Was displayed as EGL**.
Wrap CMAKE_SHARED_LIBRARY_CXX_FLAGS in quotes.

The variable is empty on some platforms (Windows), would cause issues.
Treat MagnumMathObjects and MagnumObjects libs separately for exporting.

It's more intuitive and might be useful at some point.
Fix loud linker error on mingw32.

Mingw for some reasons instantiates depending template before dependent
one, causing the dependent one to be instantiated twice.
Another mingw32 linker error fix.

This class is templated and thus doesn't export anything.
Mingw32's GCC 4.7 doesn't have std::to_string().
Yet another mingw32 linker fix.
Primitives: fix Icosphere header.

This mess is long overdue.
Primitives: remove template crap around Icosphere.

Now it has API similar to all other primitives. This thing was long
overdue.