Revert "Fix bug where hex (0x[a-f0-9]+) is output as a NUMBER and WORD"

This reverts commit ab75f3baf876b06097234fefa383dab461245d48.

Moving this to the lexer instead of scanner, since this just needs to
break down stuff into characters and such. Plaintext has no need for a
hex type. We're just NUMBER, WORD, CHAR, and WHITESPACE here.