Support boolean and number arrays

[ulken]

Background
Currently, minimist-options supports type: array. However, the values of the array are always parsed as 'string'. yargs/yargs-parser (which are minimist backwards compatible) have support for coercing values 'number' and 'boolean' as well (see opts.array under yargs-parser API).

Proposal
Therefore, I would like to see minimist-options supporting these types too.

Considerations
I have considered the following options for how that could look:

1. Add another property elementType: 'number'|'boolean' (potentially arrayElementType to tie it more to array). This would only be allowed when having type: array.
2. Extend type with support for ['number'] and ['boolean'].
3. Extend type with support for 'number-array' and 'boolean-array' (camelCasing possible if preferred).
4. Extend type with support for numbers and booleans. Note: plural.
5. Extend type with support for { type: 'array', elementType: 'number|boolean' }.

Note: Additionally, 'string' would of course be a valid element type.

#1 is explicit, but verbose, introduces an extra property which would only be valid under certain conditions (which is always a little "blah" and adds complexity).

#2 is a little magical, but I like how terse it is and find it quite expressive/intuitive when you look at it. ”Aha, it’s an array of (number|boolean)s”.

#3 would introduce magical (made-up) strings. Not very fond of.

#4 is probably the simplest of them all. My only concern is: is it distinct enough or too easy to mix up?

#5 Using an object is always neat, but having to specify type: 'array' again feels weird as it would be the only valid value, but leaving it out would be odd too.

I'm leaning towards #2 or #4.

Any other suggestions?

Backwards compatibility
To be backwards compatible and not break existing code bases, I suggest we still keep type: array and its behavior intact.

@vadimdemedes What say you?

[ulken]

@vadimdemedes Went ahead and implemented it. Hope you get around to have a look sometime soon. Would be much appreciated to have this merged (in some form). Thanks!