[tex-k] minor bugs in The METAFONTbook

[胡亚捷 (Hu Yajie)]

Page C165, line -7
The text says `zero or more undelimited parameters', but the syntax above
allows only up to one. Examples like `def f expr x,y = x,y enddef' and
`def f expr x expr y = x,y enddef' produce errors.

Page C176, line -7
The final semicolon is redundant, and it doesn't appear in the real definition
of Appendix B. (Also the colons should have Punct, not Rel, spacing.)

Page C279, lines 9 and 12
Maybe the second version number should be `2.71', to agree with page 262?
(If so, the first version number should probably be $\pi$ after Knuth's death.
I wonder if Addison-Wesley will do this...)

Appendix I, in general
`<declared variable>'
    Change `175' to `175--180'.

`empty option in for list'
    Change `171' to `171--172'.

`forbidden tokens'
    Page 173 doesn't seem to define forbidden tokens.

`loops'
    Add `171--173'.

(Does the November 1 deadline mean Knuth will start fixing the bugs
in November, so that new versions can be issued as early as possible?)

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Previous reports:
https://github.com/dine2014/texbook-mfbook-bugs/blob/master/bugs.md