Changes in 0.1.5 version:
* Minor changes to the manual.
* plot_graphAOA() now also plots the critical path. plot_crit_pathAOA() is no longer available. Check documentation and vignette.
* Added two new functions: PERT_newtime() and PERT_newprob().

Changes in 0.1.4 version:
* Added ASAP (As Soon As Possible) anad ALAP (As Late As Possible) charts.
* The vignette supplemented adequately to the changes introduced.

Changes in 0.1.3 version:
* Added the optional fixed_seed parameter to the functions that plot graphs.
* Added directive term for normal time to the list containing results for the LESS method.
* Fixed some minor bugs in the code.
