created tests to reproduce problem

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
added isBounded method to expressions to keep track of which types require special handling

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
added boundedness checks to look-behind

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
rewrote degenerate tests to expect UnboundedLookBehindException

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
consolidated look-behind tests into LookBehindProps

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
corrected copy-paste error in genIndefinite

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
expanded CharRange to allow first == last

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length
added isBounded filters to look-behind generators

GitHub issue #5 - PatternSyntaxException: Look-behind group does not have an obvious maximum length