Release process for compiled builds

[yusefnapora]

We should set up an automated build process that compiles tagged releases for linux and osx. This should be possible on Travis: https://docs.travis-ci.com/user/deployment/releases

Their mac os environments support go 1.7, so we should be good there.

TODO:

• [X] setup travis matrix build for linux and osx environments
• [X] cache the big dependencies (gorocksdb, the gx stuff, etc)
• [X] configure travis to push tagged releases to github

[denisnazarov]

Would be awesome to do this before launch. Installing gorocksdb took 10min+ on my laptop and really made going through the tutorial sad :\

cc @parkan

[yusefnapora]

we can at least manually upload binaries until we get things automated

[parkan]

Oh yeah let's cook some binaries, this should have been on the list

[vyzo]

We should also do container based setup -- the base container with the dependencies and build on top should be fast.

At any rate, let's have a fast installation procedure I can add to the README -- in fact I'll make a couple of sections and start with them (and have installation from source last, with the caveat that it is slow!)

[vyzo]

Also for binaries: I can make and sign binaries for linux and yusef can do the same for OSX. We need a place to put them though.

[parkan]

Don't need to get this in for V2, however see https://github.com/mediachain/concat/issues/59

[vyzo]

Implemented in #61