TODO

   1 - [ ] Support time ranges (i.e. reading the timeline between given time points)
   2 - [ ] Implement rfc3339->epoch and remove dependency on rfc3339-old
   3 - [ ] remove dependency on http-client
   4 - [ ] optional text wrap
   5 - [ ] write
   6 - [x] caching (use cache by default, unless explicitly asked for update)
   7   - [x] value --> cache
   8   - [x] value <-- cache
   9     requires: d command
  10 - [ ] timeline limits
  11 - [ ] feed set operations (perhaps better done externally?)
  12 - [ ] timeline as a result of a query (feed set op + filter expressions)
  13 - [ ] named timelines
  14 - [ ] config files
  15 - [ ] parse "following" from feed
  16   - following = <nick> <uri>
  17 - [ ] parse mentions:
  18   - @<source.nick source.url> | @<source.url>
  19 - [ ] highlight mentions
  20 - [ ] filter on mentions
  21 - [ ] highlight hashtags
  22 - [ ] filter on hashtags
  23 - [ ] hashtags as channels? initial hashtag special?
  24 - [ ] query language
  25 - [ ] console logger colors by level ('error)
  26 - [ ] file logger ('debug)
  27 - [-] commands:
  28   - [x] r | read
  29     - see timeline ops above
  30   - [ ] w | write
  31     - arg or stdin
  32     - nick expand to URI
  33   - [ ] q | query
  34     - see timeline ops above
  35     - see hashtag and channels above
  36   - [x] d | download
  37   - [ ] u | upload
  38     - calls user-configured command to upload user's own feed file to their server
  39   Looks like a better CLI parser than "racket/cmdline": https://docs.racket-lang.org/natural-cli/
  40   But it is no longer necessary now that I've figured out how to chain (command-line ..) calls.