Javascript bindings (#14)

* Initial version ready

- bindings are in `bindings/emscripten.cpp`
- minimal Javascript example is in `examples/ggwave-js`

* add npm package + add test-ggwave.js

* js : rename export name to "ggwave_factory"

* update to v0.1.5

* Update README.md

* npm : add npm-publish target

examples/ggwave-common-sdl2.cpp

@@ -10,7 +10,7 @@
 #include <chrono>
 
 #ifdef __EMSCRIPTEN__
-#include "emscripten/emscripten.h"
+#include <emscripten.h>
 #else
 #define EMSCRIPTEN_KEEPALIVE
 #endif