I added in the RTS mon functionality early on. It's running as separate threads. I think this is now better implemented as functions in Acton that do C magic under the hood.

One of the reasons to run as a separate thread was to be able to report on the state of things regardless of what the RTS might be doing but the biggest impediment to anything right now is the GC, which stops all threads anyway.... so I think it's OK to fold this into Acton functions instead.

• add functions in rts module to get RTS stats
  • just follow same structure as today, but return Acton objects (lists & dicts) rather than a JSON blob
  • do any conversion to JSON in Acton, if necessary
• expose information over prometheus style HTTP interface
  • requires a HTTP server in stdlib
• implement some simple prometheus CLI client
• remove rts mon socket (replaced by prometheus interface)
• add new rts monitor log actor that writes RTS stats to a file
• remove rts mon log