Updated toolchains submodule.
package: added MinGW-w64 PKGBUILD.
Added and documented Doxygen debug operator commands for enums.
Revert "Fixed compilation with GCC 4.9."

The final release doesn't have the issue with non-explicit default
std::vector constructor.

This reverts commit 05386e887a993e30d95c95dd62d856fd4a5c5f2c.

Conflicts:
	src/Utility/Directory.cpp
package: removed GCC 4.9 PKGBUILD.

Useless now, as 4.9 is in the repo.
Upgraded Doxyfile to 1.8.7.
doc: make section names unique.
doc: specify ordering of sections in detailed documentation.

It makes sense, but this ordering also helps to avoid bug in Doxygen
1.8.6+ which merges next non-xrefitem section with the previous one (so
e.g. the TODO list contained the following @see block, which is not
desired).
Containers: completed documentation review.
Interconnect: completed documentation review.
PluginManager: completed documentation review.
TestSuite: completed documentation review.
Utility: completed documentation review.
Utility: fix unaligned read also in 64-bit MurmurHash2.
Utility: stateless MurmurHash2 implementation.
Utility: renamed AbstractHashTest to HashDigestTest.

AbstractHash class is literally one typedef.
Utility: mark implicit constructor as implicit.
Utility: added constexpr HashDigest constructor.

Also testing all constexpr constructors.
Merge branch 'master' into compatibility

Conflicts:
	src/Corrade/Containers/Array.h
	src/Corrade/Utility/Test/AbstractHashTest.cpp