PluginManager: use "" for inter-project includes.
Utility: removed unused pow2() and log2() functions.

pow2() is a joke.
Utility: moved CORRADE_AUTOMATIC_* to new Macros.h file.

I need to get rid of that utilities.h file.
Utility: added CORRADE_DEPRECATED() macro.
Revert "Utility: fix MSVC warning about out-of-range value."

This now emits warning on GCC. Reverting until MSVC makes up its mind.

This reverts commit 23757430ca742830003d98d0ebb7794d5050aac6.
Interconnect: mark deprecated function as deprecated.