[CppAD] CppAD Sparsity patterns

[Brad Bell]

I have long suspected that very large vectors of standard set have a 
large overhead and are not an efficient way to represent sparsity 
patterns for large matrices.

There is now an alternative sparsity pattern in CppAD
     https://www.coin-or.org/CppAD/Doc/sparse_rc.htm
that performs better during the CppAD speed tests. See the heading 02-01 
through 02-09 on
     https://www.coin-or.org/CppAD/Doc/whats_new_17.htm
I am planning to deprecate the vector of standard sets and boolean 
sparsity patterns.

One still has the choice to use vectors of booleans or vectors of sets 
during the sparsity calculations; e.g., see internal_bool in
https://www.coin-or.org/CppAD/Doc/for_jac_sparsity.xml#internal_bool
There is an internal data structure , different from vectors of standard 
sets, that is specially designed for the sparsity calculations and is 
used when internal_bool is false.