Releasing 1.6.2

[Oscar Benjamin]

Hi all,

I want to release 1.6.2 which fixes a bunch of things:
https://github.com/sympy/sympy/milestone/56?closed=1

Two issues are unfixed though:
https://github.com/sympy/sympy/issues/19839
https://github.com/sympy/sympy/issues/19920

I'm going to go away soon (on holiday) so I want to put the release
out tomorrow. If someone else wants to fix either of those issues
right now then the fixes can go into 1.6.2. Otherwise I'll release
1.6.2 without fixing those two issues tomorrow night (something like
2300 UCT).

Oscar