simmer 3.6.0

New features:

• New subsetting operators, [ and [[, for trajectories (1847898). Think about trajectories as lists of activities and these operators will do (almost) everything you expect. As a side effect, the generics head() and tail() automatically work with trajectories also as expected.
• New length() method to obtain the number of first-level activities in a trajectory (f86375a). Useful in combination with the subsetting operators.

Minor changes and fixes:

• create_trajectory() has been deprecated in favor of trajectory() (76c1317).
• plot_resource_usage(), plot_resource_utilization(), plot_evolution_arrival_times() and plot_attributes() have been deprecated and will be removed in the next release in order to minimise dependencies (5b43f2b). We plan to release a new package on CRAN covering these features and new ones.
• All methods are now S3 methods, so that a nice intelligible error is displayed if you apply a method to the wrong object (e891045).
• All the activity management -related stuff has been removed, i.e, get_head(), get_tail(), print_activity(), get_next_activity(), get_prev_activity() (f86375a). These methods were only useful for development purposes and nobody should be using them. And it was never a good idea to directly expose external pointers.
• Clone all trajectories before passing them to the C++ core (f655cae).
• Update "Advanced Trajectory Usage" vignette.
• Update "Queueing Systems" vignette.