Compat against Connexions/cnx-epub#23
Bridge resource hash SHA1 to MD5 and allow for an existence lookup.
Use existing archived files entry when inserting resource files.
Fixes TypeError for a non-buffer interface.
Merge pull request #34 from Connexions/issue-16

Addresses #16 and bridges SHA1 to MD5
Use openstax_accounts v0.8 and update config
Install cnx-epub before cnx-archive in .travis.yml

cnx-archive now depends on cnx-epub so we need to install cnx-epub first
Merge pull request #36 from Connexions/flywheel

Prepublication, role & license acceptance and ACL entry (codename: Flywheel)
Add API Key to "trusted-publishers" group in development.ini
Stop inserting duplicate pending resources in publishing
Merge pull request #37 from Connexions/duplicate-pending-resources

Address duplicate pending resources issue
Add valdations for meatadata
Tests for validation functions
Validation for HTML content references.
Test for a successful publication of document pointer references.
Check for document pointer validity on persistence of a pending binder.