Eliminate non-ASCII characters.

Eliminate non-ASCII characters.

There are few non-ASCII characters in various code comments. A few are
typos and the rest have obvious ASCII equivalents. This commit
replaces them all with ASCII characters.

	* include/abg-diff-utils.h: Replace "’’" with "'".
	* src/abg-elf-helpers.cc: Replace "⋅" with ".".
	* src/abg-ini.cc: Replace "@êef" with "@ref".
	* src/abg-ir.cc: Ditto.
	* src/abg-tools-utils.cc: Replace "–" with "-".

Signed-off-by: Giuliano Procida <gprocida@google.com>