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This avoids ambiguity with P and Q that we were using before for both
uPreds/iProps and indexed uPreds/iProps.

Also, make our redefinition of done more robust under different
orders of Importing modules.

The rationale is that, just like the always lemmas about uPred and the frame-preserving updates for maps and iprdos, the versions with the ' are the "more specific" versions, hard-coding more assumptions in the shape of their conclusion.

Also do some minor clean up.

Now notations are pretty printed in the same way as they are parsed.
Before "let x := e1 in e2" was notation for "(fun x => e2) e1",
resulting in overlapping notations for the same thing.

We can use a named representation because we only substitute closed values. This
idea is borrowed from Pierce's Software Foundations.

The named representation has the following advantages:
* Programs are much better readable than those using De Bruijn indexes.
* Substitutions on closed terms (where all variables are explicit strings) can
  be performed by a mere simpl instead of Autosubst's asimpl. The performance
  of simpl seems better than asimpl.
* Syntactic sugar refolds better.

add basic notions of literals, unary operators and binary operators, and use them to define +, -, <=, ...

Actual proofs will end up using own and inv, and none of the notions defined in ownership.v

We should not depend on unreleased, git-only versions.
This reverts commit ee948028.

Remarks:
* eauto needs more fuel to automatically solve the side-conditions.
* ssreflect rewrite works if we do a set (φ ..) first. No idea why.

...unfortunately, that proof actually got longer because some automation no longer works