adg: use another diameter symbol by default

The UTF-8 symbol "\xE2\x8C\x80" is more semantically correct but not
backed up by the fonts (e.g. CentOS 5.4 and Windows XP). Use the
"\xC3\xB8" phi instead.
doc: update NEWS
build: bump version to 0.7.5
doc: correct bad typo in NEWS