Integreate @naderman's composer/feature-dist into composer/satis.

Possible configuration via `satis.json`:

{
    "archive": {
        "format": "zip",
        "directory": "dist",
        "prefix-url": "http://some-s3-bucket.amazonaws.com/"
    }
}

Archives are only generated when `archive.directory` is set.

Assumed defaults (unless specified):

 * format: tar
 * prefix-url is the homepage of satis
make it zip to please @Seldaek
do not overwrite an archive if we already have one
Integrate latest push by @naderman.
allow skipping for branches
CS fixes (cc @naderman)
Regenerate lock.
Add a bunch of files to ignore.
Merge remote-tracking branch 'till/integrate/feature-dist'

* till/integrate/feature-dist:
  Regenerate lock. Add a bunch of files to ignore.
  CS fixes (cc @naderman)
  allow skipping for branches
  Integrate latest push by @naderman.
  do not overwrite an archive if we already have one
  make it zip to please @Seldaek
  Integreate @naderman's composer/feature-dist into composer/satis.

Conflicts:
	composer.lock
Generate new lock file with recent composer version
Make sure unset skip-dev option does not cause an error
Merge remote-tracking branch 'upstream/master'

Conflicts:
	.gitignore