[SDK] Add CI automation for release

[bzz]

Add automation to produce a release on tag, that include next artefacts:

• content of ./sdk dir
• lookout binaries for linux/mac os

in a single archive, uploaded to GH release.

[carlosms]

in a single archive

For other src-d projects we have separate files for _darwin_amd64.tar.gz, _linux_amd64.tar.gz. I think it makes sense to keep it that way for this project, or is there any reason to tar everything together?

[bzz]

Sorry for confusion - the suggestion was not to tar different architectures!

The suggestion is: for each architecture, have a separate archive that looks like

.
├── lookout
└── sdk
    ├── README.md
    ├── event.proto
    ├── github.com
    │   └── gogo
    │       └── protobuf
    │           └── gogoproto
    │               └── gogo.proto
    ├── gopkg.in
    │   └── bblfsh
    │       └── sdk.v1
    │           └── uast
    │               └── generated.proto
    ├── service_analyzer.proto
    └── service_data.proto

(or have one more parrent dir for convenience)

[carlosms]

Reopening so we don't forget to setup GITHUB_TOKEN in Travis

[carlosms]

done