rework and document api

src/index.js

@@ -1,6 +1,6 @@
 
 export {
-  Y,
+  Doc,
   Transaction,
   YArray as Array,
   YMap as Map,
@@ -24,25 +24,23 @@ export {
   ItemString,
   ItemType,
   AbstractType,
-  compareCursors,
-  Cursor,
-  createCursorFromTypeOffset,
-  createCursorFromJSON,
-  createAbsolutePositionFromCursor,
-  writeCursor,
-  readCursor,
+  RelativePosition,
+  createRelativePositionFromTypeIndex,
+  createRelativePositionFromJSON,
+  createAbsolutePositionFromRelativePosition,
+  compareRelativePositions,
+  writeRelativePosition,
+  readRelativePosition,
   ID,
   createID,
   compareIDs,
   getState,
-  getStates,
-  readStatesAsMap,
-  writeStates,
-  writeModel,
-  readModel,
   Snapshot,
   findRootTypeKey,
-  typeArrayToArraySnapshot,
+  typeListToArraySnapshot,
   typeMapGetSnapshot,
-  iterateDeletedStructs
+  iterateDeletedStructs,
+  applyUpdate,
+  encodeStateAsUpdate,
+  encodeDocumentStateVector
 } from './internals.js'