In the docs for MatchData it mentions an example using a block:

"Crystal".match(/[p-s]/) do |md|
  md.string # => "Crystal"
  md[0]     # => "r"
  md[1]?    # => nil
end

This example doesn't work in master as it throws 'String#match' is not expected to be invoked with a block, but a block was given. This PR adds this block method in.

One thing I do have a question about is in the docs it says md.string, but running the code like that will throw a undefined method 'string' for Nil compile-time error. Adding not_nil! makes it work, but it feels weird to always have to add that in. Should this block just yield match.not_nil!? or should I also add in an update to the docs to show that usage?