Usage suggestions for positional arguments should be in index order

[kbknapp]

The order is displayed correctly everywhere except "suggested usage" (i.e. when a typo is made and the usage string is re-generated for current usage). In this string it appears in alphabetical order which can be confusing.

[kbknapp]

This line Should probably return a BTreeMap<u8, &str> where positional arguments are first in, with index as keys, and everything else is just a key_counter += 1. Or just use a FIFO queue of some type.

... Thinking out loud.

Eventually (read soon), I'd like to re-look at the use of data structures throughout clap and see if there are more efficient choices, (i.e. using perhaps using a more standard Map and just sorting only when needed)?