Use gevent to parallelize storage operations in get_tags

This is a band-aid for #614

For context, hosted from a GCE instance with GCS being the backing
store, With this patch, we are able to 'docker pull' 859 tags without a
timeout.  Prior to this patch, we were *unable* to pull anything from a
repository with 200 tags.  This is the extent of my investigation thus
far.  Unfortunately, this change is probably just a constant factor
reduction in run-time as total network round-trips still grows linearly
with tag count.
.update-copyright.conf: Automate maintenance for AUTHORS

Use my external update-copyright package [1] to maintain the AUTHORS
file.  Don't maintain the copyright blurbs though, since this project
sticks to:

  Copyright (c) 2014 Docker.
  <Apache blurb>

and doesn't list the file's individual contributors.

[1]: http://pypi.python.org/pypi/update-copyright/
.mailmap: Standardize author names and addresses

The syntax is described in the MAPPING AUTHORS section of
git-shortlog(1).  I looked for oddities and obvious duplicates in the
list of all commit authors, and added entries here that looked
reasonable to me.  When someone used multiple email addresses, I've
chosen to standardize on whichever address they used for their last
commit.  I haven't contacted any of these folks to confirm my choices.
AUTHORS: Run update-copyright.py to update this from the Git history
Fixes issue with s3/boto/gevent hanging.
fixed link to advanced docs in faq
Merge pull request #671 from bobrik/patch-1

Fixed link to advanced docs in faq
Merge pull request #670 from chuegle/master

Fixes issue with s3/boto/gevent hanging.
Use the fully qualified class name of the boto calling format.
Merge pull request #676 from justinjohnsonio/justinjohnsonio-calling-format-classname

Use the fully qualified class name of the boto calling format.
Add DRIVERS.md for implemented docker-registry drivers
Merge pull request #677 from tobegit3hub/master

Add DRIVERS.md for implemented docker-registry drivers
Changes to enable eu-central-1.
Merge pull request #678 from chuegle/master

Changes to enable eu-central-1.
Add docker-registry-driver-elliptics in DRIVERS.md
Merge pull request #679 from tobegit3hub/master

Add docker-registry-driver-elliptics in DRIVERS.md
Updated changelog and version bump
Add table of contents to README.md

To help quickly find information in the README
Fix quicklinks
Typo