added hamming distance for x history metrics, and changed structure of agents so that t_hist is now a Float64 (otherwise, conflicts happen because dt can be less that Float16 error)

Version 0.2. Changed the structure of agents, to better integrate the geotrait. Changes have telescoped to accessor get_geo that now takes t as an argument, and all the functions that are using it.

version 0.1.8, with new documentation, old competition and birth function deleted because now passed by the used.

Test have also been modified, because it seems that this change also changes the random seed.

reflected is now passed as an argument in p
an other argument "dt_saving" is introduced in p for Gillepsie, which allows one to save results every dt_saving step instead of fixed number. if not specified, only last time step is saved.