Update to 1.5, and simplify a lot.

New features in 1.5 since 1.4:

- regular expressions (with Oniguruma)

- a library/module system

- many new builtins

    - datetime builtins
    - math builtins
    - regexp-related builtins
    - stream-related builtins (e.g., all/1, any/1)
    - minimal I/O builtins (`inputs`, `debug`)

- new syntactic features, including:

    - destructuring (`. as [$first, $second] | ...`)
    - try/catch, generalized `?` operator, and label/break
    - `foreach`
    - multiple definitions of a function with different numbers of
      arguments

- command-line arguments

    - --join-lines / -j for raw output
    - --argjson and --slurpfile
    - --tab and --indent
    - --stream (streaming JSON parser)
    - --seq (RFC7464 JSON text sequence)
    - --run-tests improvements

- optimizations:

    - tail-call optimization
    - reduce and foreach no longer leak a reference to .

(wiz)