simmer 3.7.0

New features:

• New timeout_from_attribute() activity makes it easier to set a timeout based on an attribute (#129).
• The activities set_attribute(), set_prioritization(), set_capacity() and set_queue_size() get a new argument mod which, if set to "+" or "*", modifies the corresponding value instead of substituting it. This makes it easier to increment, decrement or scale one of these values (#130).
• New *_selected() versions for the already available resource getters: get_capacity(), get_queue seize(), get_server_count() and get_queue_count() (#134).

Minor changes and fixes:

• Broadcast signals with higher priority to prevent an arrival to catch its own signal with a trap() after a send() (#135).
• Generate new arrivals with minimum priority to avoid wrong interactions with simultaneous activities (#136).
• Remove v3.6.x deprecations: the old attribute retrieval system (see notes for v3.6.3), as well as methods create_trajectory() and onestep() (#117).
• Remove get_mon_resources()'s data argument. It was there for historical reasons and probably nobody was using it (851d34b).
• New vignette, "simmer: Discrete-Event Simuation for R", paper accepted for publication in the Journal of Statistical Software. Remove "Terminology" vignette (#127).
• New vignette, "Design and Analysis of 5G Scenarios", supplementary materials for a paper accepted for publication in the IEEE Communications Magazine (#137).