RF: split into Experiment and Task

RF: default validResponses are now j and f
ENH: set_paths doesn't need args
NF: unittest for non-stop autorun
NF: get_breaks to break during the run
NF: show_intro as an alias show_intructions
RF: try_makedirs, signal_det moved out from Experiment
BF: small fixes
ENH: p_corr can work on two DFs
NF: initial support for report
ENH: bumped up version to 0.5a2