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

tests/test-ggwave.js

@@ -0,0 +1,19 @@
+var factory = require('../bindings/javascript/ggwave.js')
+
+factory().then(function(ggwave) {
+    // create ggwave instance with default parameters
+    var parameters = ggwave.getDefaultParameters();
+    var instance = ggwave.init(parameters);
+
+    var payload = 'hello js';
+
+    // generate audio waveform for string "hello js"
+    var waveform = ggwave.encode(instance, payload, ggwave.TxProtocolId.GGWAVE_TX_PROTOCOL_AUDIBLE_FAST, 10);
+
+    // decode the audio waveform back to text
+    var res = ggwave.decode(instance, waveform);
+
+    if (res != payload) {
+        process.exit(1);
+    }
+});