Fix highlighting issues with numbers and hexnumbers

- Commit 9ee1681e98f7da16699225eb7849bdc03add5861 fixed the case when a variable
contains a number, but not several because the negative lookbehind only
looks one character behind. Now foo42 works

- Two issues with hexnumbers, 0x in variable names and non-greedy match were
matching inappropriately in some cases.
Also allow 0X in upper case.