Add circleci config with mac, windows and linux testing (#338)

- Add EMSDK_NOTTY variable which we can use on CI to prevent tty output.
- Add test.bat for windows which mirrors test.sh.
- Remove travis support

emsdk

@@ -10,7 +10,7 @@ base_dir=$(dirname "$0")
 
 # Look for python3 first.  This is especially important on macOS (See:
 # https://github.com/emscripten-core/emsdk/pull/273)
-python=$(which python3)
+python=$(which python3 2> /dev/null)
 if [ $? != 0 ]; then
   python=python
 fi