Private repos

[jdoklovic]

This fixes #11

These changes provide support for private repos via https basic auth and/or ssh public keys.
This also removes the reliance on github and allows using other repos (github, bitbucket, etc)

@tmrts DO NOT MERGE THIS...
To get private repos / auth working requires upstream changes. They are as follows:

• need support for hashed hostnames in crypto/ssh/knownhosts
  • A PR has been submitted to golang.org/x/crypto: https://go-review.googlesource.com/#/c/40532/
  • A matching PR has been made to src-d's fork of crypto: https://github.com/src-d/crypto/pull/2
• need support for providing credentials to BasicAuth in go-git
  • A PR has been made here: added credentials provider for basic auth src-d/go-git#353
• need gopkg.in/src-d/go-git.v4 rebased with master once these changes are pulled in

Once all of the above is complete, this PR can be merged.
In the meantime, I've vendored the dependencies in the bolir project and made the above changes to get it working. Attached is a zip file of the project with the vendored dependencies. You should be able to extract and run go install to test it out.

boilr.zip

[MrSaints]

Any updates?

[rexlv]

Any progress?

[jayrod]

So has this been implemented yet?