Dropped GCC 4.6 support.

It will now live in compatibility branch only.
Containers: removed superfluous template parameter from EnumSet.

Now that the minimal supported version of GCC is 4.7 it can be replaced
with std::underlying_type.
Add todo to use -std=c++11 instead of -std=c++0x.

Kept for compatibility with compatibility branch.
package: deleted MinGW32 PKGBUILD.

Replaced with MinGW-w64 in ArchLinux.
Properly credit all contributors.
Require C++14 support.
Utility: ability to create HashDigest directly from data.

This could be done in pure C++11, but I don't want to replicate
std::integer_sequence functionality yet again.
Utility: constexpr HashDigest comparison.
Utility: constexpr MurmurHash2 implementation.

I only had to get rid of reinterpret_cast and everything worked
flawlessly. Currently this works with Clang 3.4 only.
Utility: also this.