compat.serialize: ajust API of serialize to/from string functions
compat.serialize: ajust API of serialize to/from string functions

Add 2nd optional template param to serialize_to_str() and
serialize_from_str() and move corresponding casts inside, those, making
*_indirect functions useless (remve them).

Provide overloads for pure object pointers.

uentity/blue-sky-re,uentity/blue-sky-re,uentity/blue-sky-re