filter() function; refactor grep() to use filter() internally
sublist() function to get N elements at the head or back from the tail
uniq() function
nth() function
every(), none(), and some() context functions added
rename the internal filter() to FilterInternal() to disambiguate from FnCallFilter(); rename internal preplist() to Preplist()
fix FilterInternal() to accept calls to grep and filter
add filter() acceptance test
add sublist() acceptance test
add uniq() acceptance test
add nth() acceptance test
add every(), some(), and none() acceptance test
add filter(), sublist(), uniq(), nth(), every(), some(), and none() reference manual entries
Merge pull request #548 from tzz/tzz/redmine-2081-data-facilities

Tzz/redmine 2081 data facilities