Better support for rebar3

[kpy3]

Rebar3 is new widely adopted replacement for rebar (EOL'ed and not used in most modern apps and libs these days) and differs from it in number of ways:

• introduces concept of profiles
• more directory configuration options
• aliases
• extended application versioning

and more.

It looks like it's time to remove support for old rebar and start to implement features from rebar3, any thoughts?

[ignatov]

Hi, I have no objectives, due to a lack of time I'll be glad to have any assistance.