Serve Static Files

[bushidocodes]

Blocked by #164
Blocked by #327

We currently have a very basic HTTP web app that does PHP/CGI style templating in C. This base functionality would be considerably more useful if SLEdge could serve static assets alongside the dynamically-generated content.

localhost:8080/index.html -> resolves to a serverless function that executes to dynamically generate an HTML web site.
localhost:8080/index.css -> serves a static stylesheet that is linked from the dynamically generated HTML.
localhost:8080/index.js -> serves a static JavaScript that is linked from the dynamically generated HTML.

In order to accomplish this, we need to support:

• WASI filesystem calls
• Enhance JSON spec to specify a specific route that resolves to a serverless execution
• Optionally, if we are using the 'reactor' pattern, different routes might identify different exported functions.