Fix handling of repeats and alternative options in Tabular

[petoalbert]

I have noticed that tests in RegexSpec for atMost and between were ignored and that they would fail. In this PR I attempt to make them green.

There were two bigger areas that I fixed.

1. Handling of the | operator between Steps. In the original version, combining anything with Matched would be a Matched state as well. This would, however, reduce alternatives like aaa | aa | a to the shortest possible sequence. To help with this, I "uncommented" the MatchedOrJump type and interpreted it as some kind of "checkpoint". If in the while loop in the implementation of test we encounter a MatchedOrJump, we set returnV to the current index but otherwise continue the loop. Combining Matched with Jump(...) in this case would resuld a MatchedOrJump.

2. Handling Empty matchers: The current implementation of LookupFunction can only tell if a character matches or not. It cannot tell if it can match without consuming any input. There is an object Empty which extends Tabular, but it cannot be combined with a LookupFunction currently (Empty | lookup = lookup). This will fail for uses of atMost, or generally Repeat where 0 matches are allowed as well. To fix this, I moved Empty under LookupFunction and introduced a supportsEmpty value to LookupFunction. Combining lookup functions sequentially where supportsEmpty=true will create MatchedOrJump steps as well.

[vigoo]

Please run scalafmtAll

[vigoo]

Looks good to me, thanks!