TeX reader: replaced 'unary' with 'phantom'.
TeX reader: Rewrote ctrlseq and oneOfCommands.

ctrlseq now checks for notFollowedBy letter only in the case
of alphabetic control sequences.

That allows us to simplify oneOfCommands to use ctrlseq.
Removed some unhelpful error messages.

(The names are too internal to this package to be helpful
to users.)
Improved 'escaped'.

Now, the input

    \John

yields a better message, with information about all the things it
was looking for, not just the escapes.
Removed trailing whitespace