It encapsulates the following common pattern, used several times in
el-get to allow recipe properties to override defaults if present:
(if (plist-member plist prop)
(plist-get plist prop)
default)
This includes teaching methods that they now work with a symbolp PACKAGE,
some more cleaning up, and some load-path adjustments now that a part of the
code is in a subdirectory (methods).
Also include some of the tests used to convince oneself that the refactoring
didn't break any and all use cases for el-get, with some rough documentation
about how to use them.