Allow customizing the --version and --help messages

[porglezomp]

Fixes #889

This currently doesn't support customizing them from YAML, so it still needs some work.

[coveralls]

Coverage increased (+0.2%) to 91.792% when pulling 389c413 on porglezomp:feature/customize-version-help into cb5c9f7 on kbknapp:master.

[porglezomp]

Nice, the YAML stuff was really easy to add.

[coveralls]

Coverage increased (+0.2%) to 91.803% when pulling c5dac3f on porglezomp:feature/customize-version-help into cb5c9f7 on kbknapp:master.

[coveralls]

Coverage increased (+0.2%) to 91.803% when pulling c5dac3f on porglezomp:feature/customize-version-help into cb5c9f7 on kbknapp:master.

[kbknapp]

Looks great, thanks for knocking this out! I was a little worried about confusing people with help_message and them thinking it's analogous to App::about but then I saw your documentation 😄 This would be a super minor thing anyways so I'm fine with it. Plus there isn't really anything better, help_help invites potentially more confusion.

Thanks again! 👍 @homu r+

[homu]

📌 Commit c5dac3f has been approved by kbknapp

[homu]

⚡ Test exempted - status

[kbknapp]

Once #893 merges, I'll put out a new version on crates.io