Setup API sections references.

Scheme: api/{section}/{endpoint}.{method}
Fix references to API
Split configuring.rst into the set of articles.

Key idea is to provides complete description of all available CouchDB
configuration options grouped by their ini sections and the single place to
keep other related configuring stuff.
Describe attachments config section.
Describe vendor config section.
Describe couchdb config section.
Describe uuids config section. Tweak a bit related API section.
Describe stats config section.
Describe couch_httpd_auth config section.
Improve vhosts config docs using CouchDB sources.
Sort httpd options.
Use Paul J. Davis commit message as os_daemons docs.
Describe daemons config section.
Describe compaction config section.
Describe compaction_daemon config section.
Describe native_query_servers config section.
Describe replicator config section.
Describe query_servers config section.
Describe oauth and couch_httpd_oauth config sections.
Describe log and log_level_by_module config sections.