TODO

2021.01.24:
- WebSockets URL to command line argument
- Command line arguments for extension IDs
v How to wait until all messages are sent before closing the WS connection (2021.01.31)

2021.01.30:
v `string=` (2021.01.30)
v `unwind-protect` `with-` macro to close the connection (2021.01.31)
v wait-group (2021.01.31)
v `remove` in `filter` (2021.01.30)
- Release build with ECL

2021.01.31:
- sysexits
- Timeout