Add `complete -C swagger swagger` support

[rwxrob]

Problem statement

As a command line utility, swagger could easily benefit from detection completion context to sensing the COMP_LINE environment variable allowing all the completion code to be maintained internal as Go code and allowing bash users (the standard Linux shell) to simply add completion with a single complete -C swagger swagger command instead of sources several lines upon each new shell instantiation.

For more information, please see the "Programmable Completion" section of the bash man page.

Thank you.

😊 I'm happy to work on this if there is enough interest.

[casualjim]

yes please add this