PEP 814: Misc changes

[vstinner]

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[efimov-mikhail]

There's another typo:

"Keys must be hashable and so immutable, but values can be mutable. Using immutable values creates a hashtable frozendict." ->
"Keys must be hashable and so immutable, but values can be mutable. Using immutable values creates a hashable frozendict."

And maybe it'll be better to stress that values can not be changed (in terms of pointers/objects) but they can be mutable objects itself? This difference was not very obvious to me at the first reading attempt.

[nschneid]

"hashable and therefore immutable"?