schemas FEATURE add schema getters from the context

Also check for the duplicities in the context when parsing a new schema.
diff --git a/src/common.h b/src/common.h
index d7d17de..afd4d0b 100644
--- a/src/common.h
+++ b/src/common.h
@@ -15,6 +15,10 @@
 #ifndef LY_COMMON_H_
 #define LY_COMMON_H_
 
+#define _DEFAULT_SOURCE
+#define _GNU_SOURCE
+#define _XOPEN_SOURCE
+
 #include <assert.h>
 #include <pthread.h>
 #include <stdint.h>