CMake buildsystem fork of Jesse Kornblum's md5deep/hashdeep.

This codebase is largely the original from SourceForge's SVN repo for the same but has been pulled to here as a fork to make life easier for someone trying to use it for cross-compilation and the like. The Autotools build system was broken in several ways that it was not worth trying to fix it properly for cross-compilation- so we have the start of the fork as we've moved it to CMake.