`Regex` match methods do not accept negative position

[straight-shoota]

A negative index into a string usually means to start counting from the end ("foo"[-2..] == "oo"). This does not work for Regex's match methods though: /oo/.match("foo", -2) == nil.

I think it makes sense to add this to the implementation for consistency.

[HertzDevil]

Regex#match depends on String#char_index_to_byte_index which doesn't support negative arguments. Not sure about the rest of Regex though

[straight-shoota]

Btw. the equivalent works in Ruby: /oo/.match?("foo", -2) # => true

[HertzDevil]

There are actually two notions of an index; character indices depend on String as mentioned above, byte indices should only require single-line additions to Regex#match_at_byte_index and #matches_at_byte_index?.