Fix handle global --help flag

[straight-shoota]

Resolves #649

[ysbaddaden]

That won't catch shards --local --help for example, and shards install --help also runs the install command then prints the help 😞

[ysbaddaden]

I'm trying to find something, but it doesn't work as intended so far.

[straight-shoota]

My intent was to do a simple fix for the patch release to address the most common use case shards --help.
But the behaviour of shards install --help certainly isn't acceptable either.

I think we have the following alternative steps forward:

• Fix the regression from Forward unmodified ARGV to subcommand #631
• Revert Forward unmodified ARGV to subcommand #631 for 0.19.1 (possibly followed by a reimplementation with fixed behaviour in 0.20.0)
• Refactor the entire CLI handling code to fix it once and for all (this should be based on parsing the command first, and then decide on the possible options, like the compiler CLI does), and release this as 0.20.0

[ysbaddaden]

I think this works restores the previous behavior: #665

[ysbaddaden]

Refactoring would indeed be 👍

And having a better support for sub-commands right into OptionParser would be ❤️

[straight-shoota]

Resolved by #665