OAK-767 Implement Node#removeMixin

- remove documentation about missing implementation


git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1526345 13f79535-47bb-0310-9956-ffa450edef68
OAK-1032: SegmentMK: One SegmentWriter per SegmentNodeStore

Adjust code to use just one SegmentWriter

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1526354 13f79535-47bb-0310-9956-ffa450edef68
OAK-301 Document Oak - MongoMK
- describe document splitting

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1526417 13f79535-47bb-0310-9956-ffa450edef68