Hex package and rebar3

[Licenser]

Hi I've published pgapp to hex, this PR includes the changes that were required. If you are interested in taking the package over I'll gladly give it back :).

PS: I've added myself as a secondary maintainer there for the moment so people don't bother you with hex package related, feel free to remove that.

[davidw]

Please make changes against the devel branch, as per the README. Then we can release that. I'm more than happy to have you be the go-to person for the Hex package, although please do make sure there's a pointer to the epgsql github page and mailing list.

Thank you!

[Licenser]

there is no devel branch to make a PR against ;) but I'll put the links in the package description!

[davidw]

Oops, my apologies! I missed the 'pgapp' thing.

[Licenser]

no worries :) thanks for the swift reply!

[davidw]

I see that the rebar.config changes too... is there any way that backwards compatibility can be maintained? I haven't followed rebar3 much, unfortunately.