* The partial-evaluation of #elif sequences was broken and the
spaghetti logic of its implementation was too hard to understand.
I've re-done it using a straight-forward table-driven push-down
automaton.
* The pre-processor line parser did not allow for all of the weird
places that people might put comments, which could have caused it
to add syntax-errors to the output by removing a #if line containing
the start- or end-marker of a comment.
* The lexer didn't need to special-case the handling of string-literals
or character-constants, but it did need to learn about line-continuations
(backslash-newline).
* The input routine was buggy and bit-rotten and trivially replacable
with fgets(). I've also made the program static- and const-safe and
improved the presentation-order. The formatting of the state-transition
tables remains non-stylish.
This commit-messsage was brought to you by code-point 45.
MFC-after: one-week
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