v1.15.1

-- Fix bugs in DeleteSnirfFiles and related functions to use absolute paths without having to change current working directory. This is following the new work flow which alloows multiple groups to be loaded into Homer3 from last commit.
-- Fix bugs in demo_snirf and demo_snirf_readfile and refine demo_snirf_readfile to display clearly all fields using new SnirfClass.Info() method and the new Utils/pretty_print_struct.m function.
-- Update README and generate new snirf_homer3.
-- Small tweaks to unit test display of groupResults file paths.