This builds on top of a0d80350 (#4575)
and extends the syntax to support the token `all` or `*` to serve as
wild-card for the relaxation subject, i.e. the following non-exhaustive
list of forms is made possible (NB: the package name `all` is reserved
on Hackage):

    allow-newer: somepkg:*
    allow-newer: somepkg:all
    allow-newer: somepkg:^*
    allow-newer: somepkg:^all
    allow-newer: all:^all
    allow-newer: *:^all
    allow-newer: *:^*
    allow-newer: *:*
    allow-newer: all:all

Refer to the user's guide for details