Entering vowels with macrons

[Sean McAfee]

To my surprise, I haven't been able to find a convenient way to enter
vowels with macrons above.  Actually, the only way I've found to do so,
other than by copying and pasting, is to have the Unicode codepoints
handy and use ucs-insert.

Am I missing some way to enter these characters?  If not, what would be
the best way to add this capability for my own use?  I'm guessing that
would probably be to add the characters somewhere on the C-x 8 command
tree.  C-x 8 _ is already occupied by the two characters FEMININE
ORDINAL INDICATOR and MASCULINE ORDINAL INDICATOR, which I didn't know
existed before now and could easily do without.