Add support for OTP/23 (requires :proper update)

[flowerett]

Currently, OTP/23 is not supported due to the outdated version of the :proper library. We discovered that stack traces from exceptions raised inside prop checks are not visible.

This happens at this line: https://github.com/alfert/propcheck/blob/master/lib/propcheck.ex#L452 error got reraised inside the :proper.forall call: https://github.com/alfert/propcheck/blob/master/lib/propcheck.ex#L425

What has been discovered and done so far:

• erlang:get_stacktrace/0 is deprecated and starting from OTP/23 returns empty stack trace: https://erlang.org/doc/man/erlang.html#get_stacktrace-0

• last version of proper was released on August 21, 2018, it's outdated - https://hex.pm/packages/proper/1.3.0 With OTP/23 next macro returns an empty stack trace: https://github.com/proper-testing/proper/blob/f2b7b81666b21707244a40857cf50f4362b6e3c2/include/proper_internal.hrl#L64

• The fix for that macro is already merged to master: https://github.com/proper-testing/proper/pull/226/files

• Updating to the latest version of :proper (from GitHub) solves the problem with the missing stack trace.

• Updating to the latest version of :proper brakes a lot of tests due to some API changes, I guess there were several braking requests, so far I found this one: https://github.com/proper-testing/proper/pull/220/files

• Work for updating the :proper started in this PR: https://github.com/alfert/propcheck/pull/179 Any help or contribution is welcome!

[flowerett]

I will close this issues as it seems to be fixed, but we need to keep an eye on :proper's future changes.