Terminate TLC with a non-successful exit code when it fails to parse parameters.
Terminate TLC with a non-successful exit code when it fails to parse
parameters.

Includes minimal, non-semantic changes to main:

* Adds comments to all major blocks.
* Organizes mail sending code logically together, so that it's clear
  that it's not a precondition of calling TLC.process() or setting
  up resolvers.

[Bug][TLC]

lemmy/tlaplus,lemmy/tlaplus,tlaplus/tlaplus,tlaplus/tlaplus,tlaplus/tlaplus,lemmy/tlaplus,lemmy/tlaplus,tlaplus/tlaplus