Auto-generate MyEnumType.all() method that returns an array of all values of type MyEnumType

[elimisteve]

I would like to be able to do something like this:

enum Color {
	red green blue
}

// Implicitly auto-generated _if Color.all() is referenced in the program being compiled_, 
// and perhaps not otherwise; the user should not have to type this boilerplate! 
// Plus types can't have methods anyway, so I'm just making up this "type" syntax,
// but you get what I mean
pub fn (type Color) all() []Color {
    return [.red, .green, .blue]
}

// Also implicitly auto-generated
pub fn (c Color) str() string {
    match c {
        .red { return 'red' }
        .green { return 'green' }
        .blue { return 'blue' }
        else { return ''  // should be impossible! }
    }
}

...

if color_name_from_user_input in Color.all().map(it.str()) {
    println('Correct!')
}
else {
    println('Invalid color; guess again')
}

Then we also wouldn't have to have things like we see in vlib/compiler/main.v, as one example --

supported_platforms = ['windows', 'mac', 'macos', 'linux', 'freebsd', 'openbsd', 'netbsd',
                'dragonfly', 'android', 'js', 'solaris', 'haiku', 'linux_or_macos']
)

but could instead simply do

supported_platforms = OS.all().map(it.str())

if a str() method is also created for each enum type that returns the name of the value.
This was suggested in the docs, too, and is a great idea:

fn main() {
	mut color := Color.red
	color = .green
	println(color) // "1"  TODO: print "green"? 
}

[felipensp]

Iterator over enum values is already possible, see https://github.com/vlang/v/blob/master/doc/docs.md#values