Tab completion for sparse-checkout

[bgold09]

• Tab completion for the sparse-checkout command.
• Tab completion for the subcommands of sparse-checkout and their
  parameters.
• Addresses [Feature Request] add support for sparse-checkout #766

[bgold09]

@dahlbyk does this change look ok to you?

[bgold09]

@dahlbyk ping 😄

[bgold09]

@dahlbyk would you mind reviewing this?

[bgold09]

@dahlbyk would you mind reviewing this? All tests are passing now

[dahlbyk]

Thanks, Brian. As you can tell I've been aggressively ignoring this project, but I hope to find some time next week. Appreciate the contribution and your patience/persistence.

[bgold09]

No worries, I forgot about it too until recently