safe_memset: allow memset of zero bytes.
doc update
Simplify temporary value storage during decoding.
Simplify temporary value storage during coding.
Added check for decoding_startEnd().
simplified and optimized asn1_der_decoding_startEnd().

The second pass decoding is now avoided as the start and end
values are cached during decoding.
Added test for asn1_copy_node()
Added asn1_copy_node2()
doc update
removed unused variable