* embargo: add support for per-collection date range embargo with embargo options of 'before', 'after', 'newer' and 'older'
'before' and 'after' accept a timestamp
'newer' and 'older' options configured with a dictionary consisting of any combo of 'years', 'months', 'days'
add basic test for each embargo option
* acl/embargo work:
- support acl access value 'allow_ignore_embargo' for overriding embargo
- support 'user' in acl setting, matched with value of 'X-Pywb-ACL-User' header
- support passing through 'X-Pywb-ACL-User' setting to warcserver
- aclmanager: support -u/--user param for adding, removing and matching rules
- tests: add test for 'allow_ignore_embargo', user-specific acl rule matching
* docs: add docs for new embargo system!
* docs: add info on how to configure ACL header with short examples to usage page.
sample-deploy: add examples of configuring X-pywb-ACL-user header based on IP for nginx and apache sample deployments
* docs: fix access control page header, text tweaks
* bump version to 2.6.0b0
- don't parse json on every aclj line until key prefix matches, resulting in speed boost!
- convert aclj to dict (via cdxobject) only when match is found (disable aggregator source tracking)
