Some performance issues to be fixed

Fix #509 by checking Nan/Inf when writing a double

Travis doc is running on separated task now.

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