Add conditional expressions of the form:
foo := if lhs == rhs { then } else { otherwise }
`lhs`, `rhs`, `then`, and `otherwise` are all arbitrary expressions, and
can recursively include other conditionals. Conditionals short-circuit,
so the branch not taken isn't evaluated.
It is also possible to test for inequality with `==`.
Moves the separate quiet variable in the `Config` struct into the existing
verbosity field; the `Verbosity` enum now has a `Quiet` variant. When running, the
presence of the quiet flag will set the verbosity to `Quiet`, overriding any
number of verbosity flags in the CLI args.
Make line continuations strip leading spaces on the next line.
This changes what is passed to the shell, so this is a breaking change.
However, I don't think that this will break any recipes.
