Function pointer parameters now has names

[KoolieAid]

• Fixes Missing argument names for generated function pointers / delegates #39

Basically function pointers such as extern "C" fn(i32), the parameter doesn't have names.
In order to fix such issue, I used the alphabet to represent order

escape_name could be removed and directly put the name there since its just a-z.
although im not sure if it will break something, so i left it there

[KoolieAid]

could also go for arg1, arg2, arg3, ..., for readability instead of 1 character names

let me know if it needs changes

[neuecc]

thank you for contribution,
but your code overwrite existing parameter name.

I'll merge this PR but fix above issue and change to arg1, arg2, arg3... as you suggested.
thanks!