plugins CHANGE unify naming in plugins API

All the symbols connected with type plugins are now prefixed by
lyplg_type_ and symbols connected with extensions have lyplg_ext_
prefix.
diff --git a/src/plugins_exts_print.h b/src/plugins_exts_print.h
index 380c180..9f6fb56 100644
--- a/src/plugins_exts_print.h
+++ b/src/plugins_exts_print.h
@@ -28,7 +28,7 @@
  */
 
 /**
- * @brief YANG printer context for use in ::lyext_clb_schema_printer callback implementation.
+ * @brief YANG printer context for use in ::lyplg_ext_schema_printer_clb callback implementation.
  *
  * The structure provides basic information how the compiled schema is supposed to be printed and where. In the most simple
  * case, the provided context is just passed into ::lysc_print_extension_instance() function which handles printing the
@@ -63,7 +63,7 @@
 /**
  * @brief Print substatements of an extension instance
  *
- * Generic function to access YANG printer functions from the extension plugins (::lyext_clb_schema_printer).
+ * Generic function to access YANG printer functions from the extension plugins (::lyplg_ext_schema_printer_clb).
  *
  * @param[in] ctx YANG printer context to provide output handler and other information for printing.
  * @param[in] ext The compiled extension instance to access the extensions and substatements data.