This fixes issue #57.

I considered supporting these introduction patterns also in a nested fashion --
for example allowing `iDestruct foo as [H1 [{H1} H1 /= H2|H2]` -- but that
turned out to be quite difficult.

Where should we allow `/=`, `{H}` and `{$H}` exactly. Clearly something like
`>/=` makes no sense, unless we adopt to some kind of 'stack like' semantics
for introduction patterns as in ssreflect. Alternatively, we could only allow
these patterns in the branches of the destructing introduction pattern
`[... | ... | ...]` but that brings other complications, e.g.:

- What to do with `(H1 & /= & H3)`?
- How to distinguish the introduction patterns `[H _]` and `[_ H]` for
  destructing a spatial conjunction? We cannot simply match on the shape of the
  introduction pattern anymore, because one could also write `[_ H /=]`.

TODO: document the setup of the IntoWand and WandWeaken type classes
and the tricks using Hint Mode.

This fixes issue #67.

It now copies the hypothesis when: 1.) it is persistent 2.) when destructing
it requires a universal quantifier to be instantiated. The new behavior is
implemented using a type class (called CopyDestruct) so that it can easily be
extended.

This fixes issue #51.

This fixes issue #62.

The error message accidentally got removed in e0789039.

Unfortunately, we currently have to keep the unicode-space hack in some places because Coq still complains about the notation otherwise

This fixes issue #61.

This patch was created using

  find -name *.v | xargs -L 1 awk -i inplace '{from = 0} /^From/{ from = 1; ever_from = 1} { if (from == 0 && seen == 0 && ever_from == 1) { print "Set Default Proof Using \"Type*\"."; seen = 1 } }1 '

and some minor manual editing

For iApply and iRewrite we want that, but for iDestruct and iMod we do not.

This fixes issue #52.

This fixes issue #55.

I also renamed `iProof` into `iStartProof`, as it is supposed to be
something internal, and not a substitute of Coq's `Proof` command (as
originally intended).