types REFACTOR move integer-specific functions into a standalone source file

Split the plugins_types.c file to distinct internal implementation of
plugins types API and the (base) type plugins themselves.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3f8d53c..f1a1fad 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -134,6 +134,7 @@
     src/printer_yin.c
     src/printer_tree.c
     src/plugins_types.c
+    src/plugins_types_integer.c
     src/plugins_exts.c
     src/plugins_exts_metadata.c
     src/plugins_exts_nacm.c