Let calc_l_r_roots() special-case eyemat matrices again.
Let excitations work for r not being a special matrix.
Add zero_tol variable to mps classes. Pass on to functions that use it.
Some cleanups and removal of a debug line in tdvp_common.
ppinv solver: Improve sanity checks, make sparse solver configurable, add unit tests.
Use gmres solver by default for pseudo-inverses in excitations code.
Also be consistent about conjugates in 2-site excitations code
and clean it up a little.
Improve doc string for eps_l.
Don't supply Kp1 to calc_x when we know it is zero. Also, Cn existing does not imply existence of Kp1.
Make uniform-case CG functions less verbose by default.
Turn on symmetric canonical form by default for uniform mps.
Improve correlation_length function.
Do ensure that we still have bulk eigenvectors in restore_CF.
Add some features to sandwich go() and repair state loading a bit.
Repair whitespace damage.
Revert "Improve correlation_length function."

This reverts commit 974ed0a3853334f4c972e3211a96ba7f57cdf03a.
Redo "Improve correlation_length function" without the whitespace changes.