fix: enforce & use consistent function definitions

[hyperupcall]

Summary

In Bash, there are there ways to declare a function:

fn() { :; }
function fn { :; }
function fn() { :; }

This PR ensures that only the first form is used.

[jthegedus]

How is this deciding which files to apply to? lib/asdf.fish also has a function usage. Why is that not matched?

[hyperupcall]

How is this deciding which files to apply to? lib/asdf.fish also has a function usage. Why is that not matched?

Only bash and sh, and bats files are matched, if files are not directly supplied as arguments to checkstyle.py. Since there are relatively few lines of Fish, I opted not to do any checking of them.

[jthegedus]

Renaming the PR to be a fix: type as it touches code executed by users, so therefore should be considered as a change in the next release version.

[jthegedus]

Thanks

[Stratus3D]

Thanks @hyperupcall ! I've been wanting this for years!