LibSQL: BTree index, Heap, and Meta objects for SQL Storage layer

Unfortunately this patch is quite large.

The main functionality included are a BTree index implementation and
the Heap class which manages persistent storage.

Also included are a Key subclass of the Tuple class, which is a
specialization for index key tuples. This "dragged in" the Meta layer,
which has classes defining SQL objects like tables and indexes.

Userland/Libraries/LibSQL/CMakeLists.txt

@@ -1,8 +1,15 @@
 set(SOURCES
+        BTree.cpp
+        BTreeIterator.cpp
+        Heap.cpp
+        Index.cpp
+        Key.cpp
         Lexer.cpp
+        Meta.cpp
         Parser.cpp
         SyntaxHighlighter.cpp
         Token.cpp
+        TreeNode.cpp
         Tuple.cpp
         Value.cpp
         )