Problem: zlist_destroy crashing when using push and autofree

zlist_push actually contrary to the documentation doesn't do strdup and
therefore when destroying zlist which had some elements pushed in,
program crashes with double free during purging of items.

Solution: Add strdup where it belongs.
Made Z85 implementation dependent on libzmq version being .ge. 3.3.0
Merge remote-tracking branch 'upstream/master'
Merge pull request #851 from lovmoen/master

Problem: zarmour's z85 implementation is dependent on libzmq version
Merge pull request #850 from miska/master

Problem: zlist_destroy crashing when using push and autofree
Added missing casts in zlist selftest.
Merge pull request #852 from lovmoen/master

Problem: zlist selftest is missing explicit casts and does not compile.
Problem: API generation no longer done here (it's in ztools)

Solution: remove this from mkdoc script
Problem: selftest code uses 'tmp' as variable name

And has other style issues. Solution: fix these.
Regenerated man pages:
Merge pull request #853 from hintjens/master

Minor maintenance