added bounds to all fit functions
add option to write each bootstrap
added option to fix a seed, so that fit results are reproducable, and
fits can be done to two different things using the same bootstraps
error if bootstrap bias is larger than the eror
use fmin_slslp so we can use bounded fitting
make bounds for fit functions consistent and easier to tune
fix write each bootstrap
flip guess if guess of mass is negative
add periodic effective masses
updated some inital guesses for fit functions
added average_correlators, for averaging two correlator files config
by config
added momentum_permute, which prints all permutations of a momentum on
a lattice for a given total momentum squared
added some new read methods to pandas_reader