Remove Werror

-Werror shouldn't be used in released code since it can cause random build
failures on moderate warnings. It also depends on the used toolchain since
different toolchains may or may not print the same warnings.

CMakeLists.txt

@@ -97,10 +97,10 @@ endif( MSVC )
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   # using regular Clang or AppleClang
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Werror -Wall -Wconversion -Wshadow -Wno-sign-conversion")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wconversion -Wshadow -Wno-sign-conversion")
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
   # using GCC
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Werror -Wall -Wconversion -Wshadow -Wextra -pedantic")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall -Wconversion -Wshadow -Wextra -pedantic")
   # not yet ready for -Wsign-conversion
 endif()