Added bi-infinite, banded, symmetric, Toeplitz linear system solver.

The solver is bibst_lss and is in the utility files.
Operator.cpp was also updated to call the new linear solving routine.
Updated infinite Cholesky factorization to use "stencil" indexing.

The previous version used a "global" index which was more confusing.
Working on finite Cholesky factorization.

note: This does not compile, fix ASAP.