Updated FindCorrade.cmake and FindNodeJs.cmake from Corrade repository.
Don't use `constexpr` in Timeline.

There is no point in using this class at compile-time. Ever. Moreover
clang called through Emscripten complains that it cannot be constexpr.
Clang called normally doesn't complain, don't know why.
Method chaining in Timeline.
Emscripten: ported FindOpenGLES2.cmake and FindSDL2.cmake.

SDL headers are now included relatively.
Updated NaCl-related documentation and stuff.
MeshTools: don't create reference from rvalue.

Spotted by Emscripten/Clang, not found when running clang normally.
Platform: moved Sdl2Application event loop into separate function.

Allowing it to be called perodically from some callback.
Platform::Sdl2Application: just wait for next event.

No need to loop over when SDL has function designed to do this.
Force static build if building with NaCl's newlib.
Force OpenGL ES 2.0 target if building for Emscripten.
Method chaining in Buffer.
Added TODO.
Doxygen: ignore specific namespaces instead of whole directories.

Less maintenance burden with `#ifndef DOXYGEN_GENERATING_OUTPUT`,
removed the ones which are not needed anymore.
Removed unneeded `extern class`, added export macros to proper place.

Leftover from c4f321d91120a9cbd9269a0cf6e542447f4dd3f9, don't know at
all why and how that happen.
Doc++, TODO++
Shaders: removed superfluous `*Shader` suffix from class names.
Added some more Doxygen workarounds.

Forgotten in 3f891cfa7c0471961f9821a9cf7389acc3c98e40.
Added missing values to Mesh::Primitive.

Now we might fully support Geometry and Tessellation Shaders, hopefully.
Method chaining in Shader.

The methods return reference instead of pointer, as the class is
commonly created on the stack. Removed static functions
Shader::fromFile() and Shader::fromData(), as they are not needed now.
Also asserting that the file exists and is readable in addFile().
Platform::Sdl2Application: properly handle SDL_QUIT.

F'ed up in 6fd8dc86ada2c098b1988c0cbee84f4102095b5c, the app didn't
respond to closing the window.