GitLab

Expressed the thread-safety annotations in code, replacing the existing comment-based system (by Aaron Jacobs).

Makes gtest wokr on MinGW (by Vlad Losev); removes unused linked_ptr::release() method (by Zhanyong Wan).

Adds threading support (by Miklos Fazekas, Vlad Losev, and Chandler Carruth); adds wide InitGoogleTest to gtest.def (by Vlad Losev); updates the version number (by Zhanyong Wan); updates the release notes for 1.5.0 (by Vlad Losev); removes scons scripts from the distribution (by Zhanyong Wan); adds the cmake build script to the distribution (by Zhanyong Wan); adds fused source files to the distribution (by Vlad Losev and Chandler Carruth).