Fixing language in description of filters

Signed-off-by: Alexander Shorin <kxepal@apache.org>
Highlight possible_ancestors field for /db/_revs_diff response
Fixed typo.

Signed-off-by: Alexander Shorin <kxepal@apache.org>
Update /db/_bulk_docs docs for HTTP 417 response, examples and markup
Fix /_session section title
Fix Fauxton license bits: add missed headers, use explicit skip policy