make automated travis release

[vincenthz]

for example @tfausak had some handy script&travis stanza:

https://github.com/tfausak/rattletrap/blob/345f1d072018e072b19323311cf46043cd6af5b7/.travis.yml#L7-L8

and the upload script:

https://github.com/tfausak/rattletrap/blob/345f1d072018e072b19323311cf46043cd6af5b7/tools/upload-package.hs

[tfausak]

I'm happy to help with this! I want to write a blog post about it too :) tfausak/tfausak.github.io#132

[NicolasDP]

or one could simply use what is already available:

https://docs.travis-ci.com/user/deployment/hackage/

[vincenthz]

probably useful to see how to mix things, but as a downer using travis hackage deployment is probably going to use cabal, so caveat of no automatic generation of hpack (provided we moved to it succesfully)