feat: add error handling framework (#28)

* feat: add error handling framework

* the user would only see errors that were raised as CliError
* every other error would be a panic
* panics are also no longer displayed to users, rather human_panic
  displays how to report the issue.

* chore: update human panic message elements

* chore: bump version

bump version to v0.6.0

feat: add support for version flag

chore: bump version

upgrade version

feat: add user agent

feat: add user agent

fix: endless autocomplete

upgrade clap_complete as issue has been resolved in the package

feat: add support for postscripts (#22)

* feat(config): move to a directory-based config structure from single file-based

* feat: add support for scripts to be run after command

feat(cli): add command to view the response data of the last request (#…

…19)

* feat(http/handle_request): return more info about response other than just the body

* refactor(app_config): do not expose config fields like envs and ephenvs

* chore(app_config): make get_app_config return new AppConfig if config file not found

* feat(cli): add command to view information of the last request made

* chore: remove commented code