Scan selected `src_dirs` does not work in rebar3 environment

[vasu-dasari]

I have a project importing a lot of projects. So, I wanted sync to scan a subset of directories. So, I made my sys.conf like this:

{sync, [
    {src_dirs, {replace, [
        {"/Users/vdasari/Developer/foo/_build/default/lib/foo/src", [{outdir,"./_build/default/lib/foo/ebin"}]}
    ]}}
]}

I am using lager for logging purposes which uses lager_transform and hence compile time options for my files is quite different. rebar3 is able to figure out all the options properly. But, for sync it expects me to specify all the options for compiling my foo/src.

It would be good if sync can figure out compile-time options as well so that my sys.conf could look like this.

{sync, [
    {src_dirs, {replace, [
        {"foo/src", []}
    ]}}
]}

[vasu-dasari]

I have a PR #79 to address this issue. It works for me. Please let me know what you think?