failed to use ghc from store, it insists build from source. I gave up.

I pushed the patched code to gitlab

resolver: lts-20.26
this includes newer http-client which has the fix.

- use io-thread-pool git repo URL in stack.yaml extra-deps. no longer require
  local copy of that library.
- update docs
- add source URL in pypi metadata.

- use fast-logger to do logging
- use ExceptT to do early return
- extract getRdHandler and DB functions, code is more clean now

code removed from this repo.

sha1sum works fine with lazy ByteString.