Build PropEr using rebar3 instead of own rebar

[kostis]

This set of changes allows PropEr to be built using rebar3 instead of
its own (patched) rebar version. Besides being more modern, this
allows for easier integration of PropEr in code bases that use it as
a dependency.

Note that PropEr's version of rebar is still used for running the unit
tests, mainly due to being able to shut off more warnings than when
using rebar3. However, this only affects PropEr developers, not users.

Addresses #204 and a request by propcheck.

Obsoletes #44 and most of #168.

[alfert]

For packaging with hex, following the tutorial (https://www.rebar3.org/docs/publishing-packages),
please add this to app.src (values taken from mix.exs):

     {maintainers, ["Manolis Papadakis", "Eirini Arvaniti", "Kostis Sagonas"]},
     {licenses, ["GPL3"]},
     {link,  [{"GitHub", "https://github.com/proper-testing/proper"}]},

According to https://www.rebar3.org/docs/using-available-plugins#section-hex-package-management the hex plugin for rebar is configured globally for in ~/.config/rebar3/rebar.config:

{plugins, [rebar3_hex]}.

Publishing the package to hex can be done with rebar3 hex publish and rebar3 hex docs.

@kostis, this was the information I grabbed together from rebar docs and the mix file. Shall we put it into a separate PR?

[TheGeorge]

This file is typically checked in.

[kostis]

Why should it be? PropEr does not have any dependencies, let alone locked ones, and it seems that rebar3 automatically generates this rebar.lock file when run. What I am missing?

[TheGeorge]

rebar3 has a dialyzer command that should take care of building the plt and including the correct beams

[kostis]

I know about the rebar3 dialyzer command but I do not like it. It requires having an installed Erlang/OTP system (which I do not have) in order to find erts as an application to include in the PLT. I prefer calling dialyzer directly, and I do not see the point in not using make for these things. Note that calling Dialyzer and running the tests is for PropEr developers only, not for regular users.

[kostis]

Thanks @TheGeorge for the comments, but note that this PR is already merged. (It's of course possible to improve on it but it needs to happen in another PR.)

We want you to comment on #212 instead :-)