added basic support for serving snippets of code up to the UI

so, for example:
```
curl "localhost:7070/macros" -d'{"Type":"annotation","Dimensions":{"X":10,"Y":20,"W":100,"H":10}}'

{"Id":"4","Type":"annotation","Dimensions":{"X":10,"Y":20,"W":100,"H":10},"Content":"\u003ch1\u003eWhat Ho, Streamtools!\u003c/h1\u003e\n\u003cscript\u003e\n    console.log(\"hello\")\n\u003c/script\u003e\n"}
```