CMake will no longer complain that the minimum CMake version is not specified

Move Travis to container based infrastructure

Moved comment to the right place and added a TODO. Added another comment about the documentation task.

Set CCACHE_CPP2 environment variable to yes as described in http://petereisentraut.blogspot.co.il/2011/09/ccache-and-clang-part-2.html

Workaround clang and ccache bugs described in http://petereisentraut.blogspot.co.il/2011/05/ccache-and-clang.html

Fix #473 clang -Weverything

CMake will no longer complain that the minimum CMake version is not specified for test/CMakeLists.txt.

Abandon RAPIDJSON_NORETURN_SUFFIX