headers MAINTENANCE headers/include cleanup

- add missing extern "C" in some of the public headers for use in C++
- includes cleanup and fix ordering
diff --git a/src/parser_yin.c b/src/parser_yin.c
index 0e8c7f9..05a15be 100644
--- a/src/parser_yin.c
+++ b/src/parser_yin.c
@@ -26,6 +26,7 @@
 #include "context.h"
 #include "dict.h"
 #include "path.h"
+#include "parser_schema.h"
 #include "set.h"
 #include "tree.h"
 #include "tree_schema.h"