Overhaul of SHC passage time and inverse passage time functions

New shc_lv_transitiontime() and shc_lv_globalpassagetime(). shc_lv_passagetime() now just returns the passage time, Tp, of the stochastic region. shc_lv_transitiontime() returns the inter-passage transition time, Tt, and shc_lv_globalpassagetime() can be used to return combinations and also works with Mu.

Name of default method renamed to 'analytic' in shc_lv_passagetime() and shc_lv_transitiontime().

New shc_lv_passagetime_mu() to find the passage time, Tp as function of Mu and shc_lv_invpassagetime_mu() to find Mu as function of Tp.

Attempt at handling the off by one index issue that affects which Epsilon is a function of which Tp and vice versa for non-identical nodes (and Mu too I think), but I've not tested it.

Many other fixes and improvements.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>
Updated function to find initial conditions near SHC manifold.

shc_lv_ic() cleaned up and improved somewhat. The underlying method is the same.

Also updated README.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>