Diffs served by workhorse

First iteration; mainly pushed the branch to trigger a build.

Based on `archive.go` and `blob.go`. 

TODO:
- [x] Add the correct route
- [x] Test locally
- [x] Write tests

See merge request !45

Send timestamps when proxying

For https://gitlab.com/gitlab-com/operations/issues/264

Companion to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4278

See merge request !47

Use Go 1.6.2



See merge request !46

Purposed of this commit is to trigger CI and hope it doesn't get the
'importing internal packages not allowed' error Im getting while
building.

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/33

This reverts commit 1fa69c8d. It
turned out that the new behavior broke 'shallow git clone'.

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/36

Be compatible with GOPATH



See merge request !43

Delay HTTP headers for Git HTTP responses

Alternative to https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/38
and https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/40 .

See merge request !42

Add test guidelines



See merge request !39

Set content-length when sending git blobs

This gives the HTTP client receiving the blob a way to detect some
transmission failures.

See merge request !41

This gives the HTTP client receiving the blob a way to detect some
transmission failures.