GNU R update and manipulate Rd documentation objects

 Functions for manipulation of R documentation objects,
 including functions reprompt() and ereprompt() for updating 'Rd'
 documentation for functions, methods and classes; 'Rd' macros for
 citations and import of references from 'bibtex' files for use in
 'Rd' files and 'roxygen2' comments; 'Rd' macros for evaluating and
 inserting snippets of 'R' code and the results of its evaluation or
 creating graphics on the fly; and many functions for manipulation of
 references and Rd files.