Flags positional (consume rest)

[Vioshim]

Summary

Implemented positional for flags, this should allow to perform flags after the parameter we're intending to use while still remaining compatible with slash commands.

For example (Assuming --message is the positional flag, and defaults to "Hi" ):

?say Hello
?say Hello --ping True
?say --message Hello --ping True
?say --ping True

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[Rapptz]

The PR seems fine as-is, but do you mind adding documentation to the commands.rst file explaining this feature?