- [x] server on fixed port responding "oh no"
- [x] configurable addr
- [x] serve "index.txt" file if exists, else 404
- [ ] serve relative paths with mime type text/plain
- [ ] guess mime type
- [ ] configurable working directory
- [ ] string responses
- [ ] automatic directory index
- [ ] content ranges
- [ ] error page paths
- [ ] liquid template rendering
- [ ] upstream proxy via prefix
- [ ] upstream proxy path match
- [ ] upstream proxy header middleware rules
