Reorganize runtime header files

src/runtime/document.c

@@ -1,4 +1,4 @@
-#include "document.h"
+#include "runtime.h"
 
 struct TSDocument {
     TSParseFn *parse_fn;

src/runtime/error.cpp

@@ -1,4 +1,4 @@
-#include "parse_config.h"
+#include "runtime.h"
 #include <string>
 
 using std::string;

src/runtime/tree.c

@@ -1,4 +1,4 @@
-#include "tree.h"
+#include "runtime.h"
 #include <stdio.h>
 #include <string.h>