client CHANGE rewrite loading the schemas into context when connecting to a server

- allow setting schema callback to get schema via callers function
- change priorities: 1) searchpath, 2) callback, 3) get-schema
- schemas retrieved via get-schema are stored into the searchpath

Fixes #26
Fixes #27
diff --git a/src/session_p.h b/src/session_p.h
index d051e6d..916f2c2 100644
--- a/src/session_p.h
+++ b/src/session_p.h
@@ -125,6 +125,8 @@
 /* ACCESS unlocked */
 struct nc_client_opts {
     char *schema_searchpath;
+    ly_module_imp_clb schema_clb;
+    void *schema_clb_data;
 
     struct nc_bind {
         const char *address;