Extend Rcpp.package.skeleton to support URL and BugReports

[eddelbuettel]

This is a minor PR that adds the ability to use a 'githubuser' field which, when given, leads to URL and BugReports fields being added to DESCRIPTION. It also flips default package version to a saner '0.0.1'.

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Preferably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[Enchufa2]

Tested, works nicely.

[eddelbuettel]

Thanks for testing :) I tend to drive this from helper (command-line) script kitten.r which will take advantage of package whoami, if present, to find these fields.