Create helper functions for adjusting the config

[thisisnic]

Create helper functions so that adjusting the config can be done through something simple, e.g. set_thresholds("length", "too_short", c(300, 400)) or similar.

Also something to turn checks on and off, like activate_check("length", "too_short"), and deactivate_check("length", "too_short").

Perhaps also to save the config once done playing with, .e.g. save_config("my_custom_config.yml")

Take a look at how lintr does it