Reload modules only if their actual code changed

[fenollp]

Now that OTP can compile with +deterministic, rebar3_auto should compile modules with this option and only reload them when the generated BEAM differs from the previous one.

This is to avoid code:purge killing our processes on editing specs, comments...

This needs a rebar.config option taking either a UseDeterministic :: boolean() or ExcludeFromDeterministic :: [module()], defaulting to false (option disabled).

[vans163]

rebar_agent:do(compile) is used to compile, this ticket should be cross filed to rebar as its a rebar issue.

[vans163]

Give this a new try please, r3:do(compile) is used now. v0.5.1 of rebar3_auto