Easy stackalloc support

[Xyncgas]

Add a keyword or CE or something to create a span / IsByRefLike struct that let me yield also ByRefLike struct inside, let me pass those around to other function, then further processing the stuffs creating more ByRef stuff by giving Seq/List/Array/Map/Set modules toSpan function

[vzarytovskii]

Please, create a language suggestion (or find existing one).
Thanks.