added option "gs" for plotting, adding a gradient of colour for "3dgeo" and "3d" option in plotting, added arithmetic and geometric smoothing

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.

added function clean_world, and beta and alpha diversity ( to be continued). Modified Plots.plot, mainly for integrating the geotrait into option "x" and "xs"

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

Changes on type Agent, that is now Agent{T,U}. Added a function increment! for type Agent{MixedAgent,U}.

Introducing new abstract type to distinguish between different types of agents : continuous, discrete or mixed.

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.

Agent file: work in progress, we should remove competition kernel and carrying capacity
Gillepsie: modified updates to use kernel that we now pass as arguments through the parameter dictionary p
runworld: for now we only modified std update but this should be done for all the project

We have modified Agent file with carrying capacity and competition kernel using pdf funtion from Distributions.jl
However this will soon change.