initial implementation of OPML provider tree import
modifying provider tree import to suit OPML format
corrected fixture for provider tree import unit test
Merge branch 'provider-tree-import'

Rebasing and merging pull request #115
standardize on :providers array for supplying provider ids to queries
document providers addition
Merge pull request #116 from pophealth/provider_id

standardize on :providers array for supplying provider ids to queries
Improved support for different provider ids on OPML import

Any attribute that is assigned to a provider in the OPML will now
be pulled in as a CDAIdentifier where the root is set to the attribute
name and the extension is set to the value of the attribute.
Merge pull request #119 from pophealth/improved_provider_import

Improved support for different provider ids on OPML import
Adding children to the show action on provider

If there are children providers for a provider that is requested via
show, they are now included in a child property.
Providing documentation with Apipie
Merge pull request #120 from pophealth/improved_provider_api

Improved provider API