[CppAD] CppAD change of release directory names

[Brad Bell]

CppAD is converting its release directory names to agree with the 
corresponding CppAD version number; i.e., using year, month, and date in 
the version number. (This has been OKed by the coin-tlc.)

Currently, if you view
    https://projects.coin-or.org/CppAD/browser/releases
you will see both the old and new directory names.

The following release directories are deprecated and will be removed soon
    2.0.0, 2.0.1, 2.2.0, 2.3.0, 2.3.1

A similar change will be made to the stable directories
    https://projects.coin-or.org/CppAD/browser/stable

If you are using any of these directories, the CppAD timeline
    https://projects.coin-or.org/CppAD/timeline
can be used to determine what the corresponding new directory name is.