UPDATE: Adds 'user model' API (#27)

* bump version for documentation
* Fixes wrong doc comment
* renames old APIs to be consistent

base/src/test/user_model/mod.rs

@@ -0,0 +1,9 @@
+mod test_add_delete_sheets;
+mod test_clear_cells;
+mod test_diff_queue;
+mod test_evaluation;
+mod test_general;
+mod test_rename_sheet;
+mod test_row_column;
+mod test_styles;
+mod test_undo_redo;