Text: improve AbstractFont documentation.
Text: test line advance behavior when rendering scaled text.

Currently the test fails, because line advance doesn't take text size
into account.
Text: fix rendering of scaled multi-line text.

Take text size into account when advancing lines. I would probably not
run into this issue if I would visually test this on anything else than
unscaled pixel art font.
Text: minor cleanup.
Text: harden and clean up Renderer test.
Text: test that proper index type is used in Renderer.

Something smells fishy here.
Text: it's totally fine to have 256 vertices indexed with UnsignedByte.
Text: fix array index type in Renderer.

When we have 256 vertices and >256 indices, we need more than 8 bits to
index the index array. The tests are passing again.
Added colour uniform to flat shader (event when texturing is enabled)
This enables blending and transparency
Default colour is white (and fully opaque)
Use "" instead of <> for inter-project includes.
Updated FindCorrade.cmake from Corrade repository.
Work around missing types in NaCl's `gl2.h`.
Shaders: oops.
Text: actually have some sane default plugin dir.
Text: fix error in fontconverter utility documentation.
Math: work around missing std::round() in NaCl newlib.

Also test that our implementation behaves the same.
Platform: add at least some support for wheel events to NaClApplication.

In NaCl the wheel event is something completely different than mouse
event and in my opinion overly complicated (the scrolled distance is
measured in pixel precision!).

To preserve at least some compatibility with other toolkits, the events
are shoved into normal MouseEvent. Sadly the event doesn't contain any
position information.
external: updated Optional with Native Client support.