Parse inplace configuration names in lexer.

Parse inplace configuration names in lexer.

Make re2c do all the dirty work instead of barely recognizing
configuration-like lexeme and manually matching the lexeme against
all allowed configuration names.

This commit adds many new tokens, which means that re2c-generated lexer
and bison-generated parser have both become larger. The difference
is not as great as one might expect: ~60 Kb -> ~80 Kb in both cases.