Add stack tests
Add queue tests
Remove unnecessary PROTECT
Use .Call directly from methods
Make mpush set s correctly
Remove unnecessary duplicate
Rename last to last2
Add madd and mpush tests
Add 'C' to the end of all C functions
Rename madd and mpush functions over add and push
Fix C tests to reflect new behavior
Simplify pairlist type checks
Add push_listC and append_listC function
Simplify push and add functions
Update tests
Remove unused C functions
Add tests for push_list and append_list