After discussing this with Ralf, again, it turned out that using a bar
instead of a turnstyle would be better. When formalizing type systems, one
often wants to use a turnstyle in other notations (the typing judgment),
so having the turnstyle in the proofmode notation is confusing.

Fixes issue #85

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

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

The old choice for ★ was a arbitrary: the precedence of the ASCII asterisk *
was fixed at a wrong level in Coq, so we had to pick another symbol. The ★ was
a random choice from a unicode chart.

The new symbol ∗ (as proposed by David Swasey) corresponds better to
conventional practise and matches the symbol we use on paper.

FDor editors that display 0-width space with more than 0 width, this makes the indentation of assertions more consistent

newline before the first context" and "shuffle 0-width spaces around so
they are distributed more evenly"

This reverts commits e3c56f9e and
7fc1124c, which are workarounds for
Coq bug https://coq.inria.fr/bugs/show_bug.cgi?id=4675

Also, this commit fixes the levels to avoid parantheses.

Pros:
* It does not matter how editors render the 0-width space, everything is always aligned
* In ProofGeneral, there is no more incorrectn indentation of the first line

Cons:
* There is an empty line between the bar ending the Coq context, and the first Iris hypothesis