Add --unicode option to control how unicode characters are handled by display tools.

	* nm.c: Add --unicode option to control how unicode characters are
	handled.
	* objdump.c: Likewise.
	* readelf.c: Likewise.
	* strings.c: Likewise.
	* binutils.texi: Document the new feature.
	* NEWS: Document the new feature.
	* testsuite/binutils-all/unicode.exp: New file.
	* testsuite/binutils-all/nm.hex.unicode
	* testsuite/binutils-all/strings.escape.unicode
	* testsuite/binutils-all/objdump.highlight.unicode
	* testsuite/binutils-all/readelf.invalid.unicode