Cmake now builds with CMAKE_BUILD_TYPE=Release by default, both while

being invoked from the main Makefile (via cmakebuild) or directly from
the build/cmake directory. Suggested by @pdknsk (#1081).

build/.gitignore

@@ -18,3 +18,14 @@ Studio*
 
 # CMake
 cmake/build/
+CMakeCache.txt
+CMakeFiles
+CMakeScripts
+Testing
+Makefile
+cmake_install.cmake
+install_manifest.txt
+compile_commands.json
+CTestTestfile.cmake
+build
+lib