Fix CommunityRest#download

Returns path from extracted dir that ends with cookbook name instead the
first filename.
Verify archive content contains a cookbook and add comments.
Merge pull request #1123 from mjcdiggity/fix-community-download

Fix community cookbook download error
bump required solve version
bump required berkshelf-api version
bump required berkshelf-api-client dep
use celluloid for threaded cookbook downloads
set celluloid log level to ERROR instead of FATAL
Merge pull request #1127 from berkshelf/threaded-downloads

use celluloid for threaded cookbook downloads
link authors to the core team wiki page
version bump 3.0.0
Celluloid requires at least 2 cores
Merge pull request #1129 from berkshelf/sethvargo/min_cpus

Celluloid worker pool requires at least 2 cores
version bump 3.0.1
Update README.md

updated tested rubies
Update README.md

remove warning from Berks 2.0
minimum viable depsolving exception handling fix

If you typo the "chef-client" cookbook as "chef_client" this code
produces:

  Unable to satisfy constraints on package chef_client, which does not
  exist, due to solution constraint (sk_role_base = 0.0.16). Solution
  constraints that may result in a constraint on chef_client:
  [(sk_role_base = 0.0.16) -> (chef_client >= 0.0.0)]
  Missing artifacts: chef_client
  Demand that cannot be met: (sk_role_base = 0.0.16)
  Unable to find a solution for demands: sk_role_base (0.0.16)

Previous code only prints:

  Unable to find a solution for demands: sk_role_base (0.0.16)

Which is useless to figure out you need to fix.
Merge pull request #1136 from lamont-granquist/lcg/patch-error-handling

Handle exceptions from dep-selector
update help description for version command
update installation instructions for Chef-DK