types: Status: improve parsing and error reporting

src/types.jl

@@ -5,8 +5,8 @@ struct Status
 
     # FIXME: error codes
     function Status(ma::Char, mi::Char, meta::String)
-        '1' <= ma <= '6' || throw("Invalid")
-        '0' <= mi <= '9' || throw("Invalid")
+        '1' <= ma <= '6' || throw("Invalid: first status out of range")
+        isnumeric(mi) || throw("Invalid: second status not a number")
         if length(meta) > 1024
             throw("Invalid")
         end