PR: Add smallest normal to finfo class (#194)

Author: steff456

spec/API_specification/data_type_functions.md

@@ -95,6 +95,8 @@ Machine limits for floating-point data types.
             -   largest representable number.
         -   **min**: _float_
             -   smallest representable number.
+        -   **smallest_normal**: _float_
+            -   smallest positive floating-point number with full precision.
 
 (function-iinfo)=
 ### iinfo(type, /)