Porting add_param and rm_globalevent

[gvegayon]

This pull request includes several changes to improve the functionality and documentation of the epiworld package. The most notable changes involve the addition of new methods for handling parameters and the renaming of global actions to global events.

Key Changes:

New Methods for Handling Parameters:

• Added add_param and add_param_cpp functions to allow adding parameters to models. (R/cpp11.R, R/model-methods.R, src/cpp11.cpp, src/model.cpp) [1] [2] [3] [4] [5] [6]
• Updated the NAMESPACE file to export the new add_param method. (NAMESPACE) [1] [2]

Renaming Global Actions to Global Events:

• Renamed all references of "global actions" to "global events" in the documentation and function names to better reflect their purpose. (R/global-actions.R, man/global-events.Rd) [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

These changes enhance the functionality of the epiworld package by adding new methods for parameter handling and improving the clarity of global event-related functions.

[apulsipher]

lgtm