This commit describes the "->" notation for dependency types in
greater detail, and uses g++ to provide examples of all six cases
(although the host->target and target->target examples are a bit
artificial).
It also adds three more rows to the table for the "->*" dependency
types for non-compiler-like packages; these dependency types were
already present in the documentation but the "*" was not really
explained.
Lastly, this commit adds a hyperlink to the table from the place where
it is mentioned in the "specifying dependencies" chapter.
c9d66a7fff