Nested user bindings

[adnrivera]

Implements some suggestions on this comment.

Allows the user to write nested commands, including commands with query placeholders.

Config example

[user_bindings]
work = { command = "gh facebook", description = "Work GitHub" }
gh = { command = "gh mycompany/main-repo", override = true }

[user_bindings.aoc]
url = "https://adventofcode.com"
[user_bindings.aoc.nested.r]
url = "https://www.reddit.com/r/adventofcode/"
[user_bindings.aoc.nested.j]
url = "https://github.com/jrodal98/advent-of-code"

CLI

Server