Merge branch 'new_star' into 'master'
Use symbol ∗ for separating conjunction. 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. See merge request !21