Always put const at the beginning

[Chlumsky]

To avoid errors, I have put the const keyword for references of uknown types to the safe spot after the type name. However, this is somewhat inconsistent and it is a general convention to have it at the beginning whenever possible. Since pointer and reference types are not supported and static array types do not use references (this part is resolved), I believe it would actually be safe to put const back at the beginning without changing anything else. It also needs to be updated in the standard library API's and the Readme file. Is it a good idea though? How about normalizing it the other way around (always putting const in this position)?

[Chlumsky]

Fixed for TypeName::constRefArgDeclaration in da46380, which is used for serializer function signatures. API templates remain unchanged for now, which I think is OK, as they don't have sufficient information about underlying type.