Use Go 1.5.3



See merge request !33

Add DESTDIR support to "make install"

Fixes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/8

See merge request !27

Use gitlab-zip-cat to send zip entries

Fixes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/17

See merge request !31

Configure URLPrefix before building routes

Fixes #19 

See merge request !32

Add support for new artifacts features

It is proof of concept implementation that misses following:

- [x] Saving metadata to file, and passing that file to rails,
- [x] Making it look nice,
- [x] Have `refactor-upstream` merged: https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/20
- [x] Add tests for metadata and single file downloads,
- [ ] Spawning separate process to verify zip archive **ONHOLD**: https://gitlab.com/gitlab-org/gitlab-workhorse/issues/17,
- [ ] Spawning separate process to download file from zip archive **ONHOLD**: https://gitlab.com/gitlab-org/gitlab-workhorse/issues/17


See merge request !28

This test duplicates some of what is in internal/artifacts but
@grzesiek and I felt it was important to have an integration test that
also covers the route to this resource.

Uses escaper from mime/multipart/writer.go.

* commit '3bbb1be7':
  Version 0.6.0
  Gotta commit those moved files
  Develomentmode ended up the wrong way around
  Move test helpers into seperate package
  Prevent package testing from going into the build