Add list templates

[probably-neb]

Adds the ability to list templates (enhancement #35 ) using a flag with tthe existing flavours list command.
example usage is shown below

❱ flavours list --templates
alacritty amfora binary-ninja blink ...

globbing still works, and -t works as short for --templates as you'd expect

❱ flavours list -t "i3*"
i3 i3status i3status-rust

including the '/templates/' (or just '/' as shown later) lists subtemplates

❱ flavours list -t "i3*/templates/*"
i3/bar-colors i3/client-properties i3/colors i3/default i3/nebi3 i3status-rust/default i3status/default

note adding the .mustache extension to the end of the glob will produce the same output and is therefore optional
also note that the intermediary '/templates/' is NOT included in the output. This was done on purpose to make it easier to read, however I can imagine it causing some confusion because the output doesn't represent the actual file structure. I'm happy to figure out a different solution if this is a concern

To make it easier I made it so globs with a single '/' have the slash expanded to '/templates/' .

❱ flavours list -t "i3*/*"
i3/bar-colors i3/client-properties i3/colors i3/default i3/nebi3 i3status-rust/default i3status/default

[devhell]

OMG, @probably-neb this is amazing! Thank you! 🍻

[Misterio77]

This looks awesome and fits perfectly.

Thanks a lot, and sorry for the wait!

[Misterio77]

Merging now, thanks again!
(Pushed to fix some conflicts)

[devhell]

Thank you very much @probably-neb and @Misterio77 🍻 😄