Sometimes we need to override *parts* of a prticular profile on a project-specific base. To a novice
lein user, it is likely not clear how to achieve this. This tip points her in the right direction -
using a composite profile with a "personal" part that can be overriden in `profiles.clj` to change
what is in the "common" part of the profile.
While "Declaring Profiles" states that "Profiles specified in `profiles.clj` will override
profiles in `project.clj`," some less attentive reader can interpret it so that *keys/values* from profiles.clj override those from project.clj, not that the profile as whole is replaced. This changes
tries to make it really clear. (Of course feel free to change the wording as you see fit.)
You can now overide :default in your project.clj to change what profiles are
active when none are specified. As part of this change, default is no longer
used to for built-in settings; these are now stored in the :base profile.
This makes it possible to override :default while still including the :base
profile.
if a profile value is a vector, then combine the values using
combine-profiles. this allows you to remove duplication by putting
shared configuration in "base" profiles.
