Improve printing of arbitrary precision integers by io.print etc.

library/stream.string_writer.m:
	Make the print family of predicates print the decimal representation
	of integer/0 values instead of their underlying representation.

library/io.m:
	Update the documentation of io.print to conform to the above change.

	Fix a typo: s/hander/handler/

NEWS:
	Announce the above change.

tests/hard_coded/Mmakefile:
tests/hard_coded/print_bigint.{m.exp}:
	Test printing of integers with io.print.