Replica Format

       overview

        $URL
           /<db-uuid>/
               /replica-uuid
               /latest-sequence-no
               /replica-version
               /cas/records/<substr(sha1,0,1)>/substr(sha1,1,1)/<sha1>
               /cas/changesets/<substr(sha1,0,1)>/substr(sha1,1,1)/<sha1>
               /records (optional?)
                   /<record type> (for resolution is actually _prophet-resolution-<cas-key>)
                       /<record uuid> which is a file containing a list of 0 or more rows
                           last-changed-sequence-no : cas key

               /changesets.idx

                   index which has records:
                       each record is : local-replica-seq-no : original-uuid : original-seq-no : cas key
                   ...

               /resolutions/
                   /replica-uuid
                   /latest-sequence-no
                   /cas/<substr(sha1,0,1)>/substr(sha1,1,1)/<sha1>
                   /content (optional?)
                       /_prophet-resolution-<cas-key>   (cas-key == a hash the conflicting change)
                           /<record uuid>  (record uuid == the originating replica)
                               last-changed-sequence-no : <cas key to the content of the resolution>

                   /changesets.idx
                       index which has records:
                           each record is : local-replica-seq-no : original-uuid : original-seq-no : cas key
                       ...

       Inside the top level directory for the mirror, you'll find a directory named as a hex-
       encoded UUID.  This directory is the root of the published replica. The uuid uniquely
       identifes the database being replicated.  All replicas of this database will share the
       same UUID.

       Inside the <db-uuid> directory, are a set of files and directories that make up the actual
       content of the database replica:

       "replica-uuid"
         Contains the replica's hex-encoded UUID.

       "replica-version"
         Contains a single integer that defines the replica format.

         The current replica version is 1.

       "latest-sequence-no"
         Contains a single integer, the replica's most recent sequence number.

       "cas/records"
       "cas/changesets"
         The "cas" directory holds changesets and records, each keyed by a hex-encoded hash of
         the item's content. Inside the "cas" directory, you'll find a two-level deep directory
         tree of single-character hex digits.  You'll find  the changeset with the sha1 digest
         "f4b7489b21f8d107ad8df78750a410c028abbf6c" inside
         "cas/changesets/f/4/f4b7489b21f8d107ad8df78750a410c028abbf6c".

         You'll find the record with the sha1 digest "dd6fb674de879a1a4762d690141cdfee138daf65"
         inside "cas/records/d/d/dd6fb674de879a1a4762d690141cdfee138daf65".

         TODO: define the format for changesets and records

       "records"
         Files inside the "records" directory are index files which list off all published
         versions of a record and the key necessary to retrieve the record from the content-
         addressed store.

         Inside the "records" directory, you'll find directories named for each "type" in your
         database. Inside each "type" directory, you'll find a two-level directory tree of single
         hexadecimal digits. You'll find the record with the type <Foo> and the UUID
         "29A3CA16-03C5-11DD-9AE0-E25CFCEE7EC4" stored in

          records/Foo/2/9/29A3CA16-03C5-11DD-9AE0-E25CFCEE7EC4

         The format of record files is:

             <unsigned-long-int: last-changed-sequence-no><40 chars of hex: cas key>

         The file is sorted in asecnding order by revision id.

       "changesets.idx"
         The "changesets.idx" file lists each changeset in this replica and provides an index
         into the content-addressed storage to fetch the content of the changeset.

         The format of record files is:

             <unsigned-long-int: sequence-no><16 bytes: changeset original source uuid><unsigned-long-int: changeset original source sequence no><16 bytes: cas key - sha1 sum of the changeset's content>

         The file is sorted in ascending order by revision id.

       "resolutions"
         TODO DOC RESOLUTIONS

   BUILD
       Open a connection to the prophet replica source identified by "$self-"url>.

   replica_version
       Returns this replica's version.

   set_replica_version
       Sets the replica's version to the given integer.

   uuid
       Return the replica's UUID

Internals of record handling

   changesets_for_record { uuid => $uuid, type => $type, limit => $int }
       Returns an ordered set of changeset objects for all changesets containing changes to this
       object.

       Note that changesets may include changes to other records

       If "limit" is specified, only returns that many changesets (starting from record
       creation).

   begin_edit
       Creates a new Prophet::ChangeSet, which new changes will be added to.