Add to grammar syntax for specifying flow rates on block inputs and outputs.

[tmcphillips]

No description provided.

[tmcphillips]

One option would to allow optional cardinality qualifiers on port names, optionally within square brackets. For example an input that receives zero or one items per execution of a block could equivalently be given as:

@in optional_input?
@in optional_input[?]
@in optional_input[0-1]

An output that produces one or more outputs could be written as:

@out one_or_more+
@out one_or_more[+]
@out one_or_more[1-n]

And an input that takes zero or more items per execution:

@in zero_or_more*
@in zero_or_more[*]
@in zero_or_more[0-n]

An output that produces exactly 2 items per execution:

@out exactly_two[2]

And an input takes three to five items:

@in three_to_five[3-5]

[tmcphillips]

Paired curly braces could be supported as well in cases where square brackets imply array indexing.