if summary = FALSE (default), a matrix where the columns represent all mating days and the rows
represent all individuals in the population. If summary = TRUE, a named vector where each index gives the
number of receptive individuals on a given day and is named by the day it represents. If a matrix, the value at position
[i,j] will be TRUE if individual j was receptive on day i
If scene is a multi-year matingScene, then receptivityByDay will return a list of matrices
(as described above) where each matrix represents one year.