More consistent with what's done elsewhere, reduces header dependencies,
allows me to (later) make this independent on the AL library and also
works around a Doxygen bug. Win win!
`char*` is now the default type for byte arrays. Results in shorter
code, less annoyances and more convenient testing. As is the case with
Corrade, I'm not doing any compatibility/deprecation layer, as most of
these functions is not widely used anyway.
Everything what was in src/ is now in src/Corrade, everything from
src/Plugins is now in src/MagnumPlugins, everything from external/ is in
src/MagnumExternal. Added new CMakeLists.txt file and updated the other
ones for the moves, no other change was made. If MAGNUM_BUILD_DEPRECATED
is set, everything compiles and installs like previously except for the
plugins, which are now in MagnumPlugins and not in Magnum/Plugins.