Rename `pk.calc.aucint()` to `pk.calc.auxcint()` and generalize its use for AUC or AUMC

[billdenney]

The current code for pk.calc.aucint() and pk.calc.aumcint() are nearly identical only changing the integration functions (

pknca/R/aucint.R

Lines 183 to 185 in aac6a30

	fun_linear = aucintegrate_linear,
	fun_log = aucintegrate_log,
	fun_inf = aucintegrate_inf

and

pknca/R/aucint.R

Lines 528 to 530 in aac6a30

	fun_linear = aumcintegrate_linear,
	fun_log = aumcintegrate_log,
	fun_inf = aumcintegrate_inf

).

Please:

1. Rename pk.calc.aucint() to pk.calc.auxcint() and add the integration functions as arguments (

   pknca/R/aucint.R

   Line 30 in aac6a30

   pk.calc.aucint <- function(conc, time,

   ).
2. Create new, simpler pk.calc.aucint() and pk.calc.aumcint() functions that use the new pk.calc.auxcint() function with the correct integration functions.

[billdenney]

FYI, the other derived aumcint functions (such as pk.calc.aumcint.last()) should be retained as-is.