P1878R1 Constraining Readable Types

Instructions to change section names were ignored; the shorter section
names are preferable, and the inclusion of 'iterator.' seems sufficient
to indicate that we're talking about indirect reading and writing.

Also fixes NB US 263, US 264, US 268 (C++20 CD), and LWG3279.

Author: zygoloid

source/algorithms.tex

@@ -222,13 +222,13 @@
 If \range{a}{b} denotes a range,
 the semantics of \tcode{b - a} in these cases are the same as those of
 \begin{codeblock}
-iter_difference_t<remove_reference_t<decltype(a)>> n = 0;
+iter_difference_t<decltype(a)> n = 0;
 for (auto tmp = a; tmp != b; ++tmp) ++n;
 return n;
 \end{codeblock}
 and if \range{b}{a} denotes a range, the same as those of
 \begin{codeblock}
-iter_difference_t<remove_reference_t<decltype(b)>> n = 0;
+iter_difference_t<decltype(b)> n = 0;
 for (auto tmp = b; tmp != a; ++tmp) --n;
 return n;
 \end{codeblock}