v0.5.0-alpha.4: Chart repo index fetcher is moved to a background job

Due to a massive overhead that happened as a consequence of a heavy
chart repo index request pattern (introduced in 0.5.0), application and
installation controller latencies spiked up.

This change is aiming to get rid of ad-hoc repo index fetch approach and
move this heavy operation to a background job.

From now on, every repo instance start polling chart repo index every 10
seconds. Once the data is successfully fetched, it is preserved as a
repo attribute unmarshalled. The first fetch is blocking: assuming
Shipper starts cold, there is no previous cache we can rely upon (it
starts in a new container). On top of it, index data is never cached on
the disk as there is no use for it any longer: in-memory only.

If repo fails to fetch repo index, it behaves quite naively: simply
spins next iteration with the same delay.

Signed-off-by: Oleg Sidorov <oleg.sidorov@booking.com>

v0.5.0-alpha.2: ci: sort out our release artifacts

First of all, let's not build for every platform under the sun, it takes
a ton of time for no particularly good reason.

Second of all, let's be a little bit less verbose, we don't need to know
precisely which packages were used to compile a binary, over and over
again.

Last but not least, point travis to the actual artifacts we built. If we
build *.tar.gz, let's not try to upload all those inexistent *.tgz files
;)

v0.1.0

First release of Shipper!

Check out our announcement blog post, or the docs.