Reassigning builtins

[dloscutoff]

• XA should be the "alphanumeric" regex (-`[0-9a-z]`). XZ can be the "any letter" regex (-`[a-z]`).
• ** should be removed: E is shorter most of the time, and sometimes one wants to do "fold each on multiplication" (currently $* *, could be $** if ** weren't a token).
• @* should potentially be changed, for similar reasons ("get first of each" is currently @ *, could be @*). Maybe @/? With binary @, it's inverting something and using it as an index; with unary @, it's inverting something and getting its first character (or the first element of an inverted list, although that could just as easily be /@). Both seem like they could theoretically be useful in some situation, but I can't think of one.
• TBD on removing ++ and -- (in theory, ++ could be useful in a regex expression like XX+ +XD, though I've never had that situation come up).