Merge pull request #144 from muelleki/141-man-roxygen-case

141 man roxygen case
New parameter .id for rdply() to specify name of .n column; fixes #142
update Rd
update NEWS
Generate .id column as factor in ldply(); fixes #137
Merge branch '142-rdply-id' of github.com:muelleki/plyr into 142-rdply-id