Add Makefile to project

[jharshman]

Add Makefile(s) to project. Tweak TravisCI to use the makefile targets. Remove Circle CI as it currently only duplicates work.

• Developers test and build using the same commands the CI system will execute.
• Leverage github.com/mitchellh/gox to cross compile for different architectures.
• Generator builds drop into ./bin directory.

Resolves:
#936
#876

[umarcor]

I'm not sure about what are you trying to define in Travis. Four jobs are being inferred from the go matrix. An additional job is added to execute make fmt only with go version 1.12.x only. And a last job is added to run make test only with a single go version.

I think that make test can be added in the diff stage. Furthermore, I'd just remove the jobs: include and run make all on four jobs.

[umarcor]

@jharshman, how about adding 1.13.x?

[jharshman]

@umarcor Well right now it's testing tip which I assume is the latest and greatest version of Go.
Currently I' considering the following -

• Removing Circle CI as it seems repetitive.
• To what degree do we care about running tests against older versions of Go? i.e: 1.13.x is out, do we care about testing 1.10.x?

[umarcor]

@umarcor Well right now it's testing tip which I assume is the latest and greatest version of Go.

1.13.x was released last month: https://blog.golang.org/go1.13. tip is currently 1.14.x.

• Removing Circle CI as it seems repetitive.

Agree. Precisely, I would remove Travis too, and go with GitHub Actions. I can merge this with #968.

• To what degree do we care about running tests against older versions of Go? i.e: 1.13.x is out, do we care about testing 1.10.x?

Officially, the two latest versions are supported: https://golang.org/doc/devel/release.html#policy. Hence, neither 1.10.x nor 1.11.x are supported. Precisely, that's the motivation not to care about deprecating both of them in #876. Should you decide to remove them, please consider adding #876 to 1.0.0.