Track changes in expl3:
 - \prg_case_int:nnn => \int_case:nnn
 - \prg_case_str:nnn => \str_case:nnn
 - \str_if_eq:xx(TF) => \str_if_eq_x:nn(TF)
Use a proper l3keys approach to key aliases
Merge pull request #142 from josephwright/master

Changes to track expl3