test coverage for GNU R packages

 Track and report code coverage for your package and (optionally)
 upload the results to a coverage service like 'Codecov' <http://codecov.io> or
 'Coveralls' <http://coveralls.io>. Code coverage is a measure of the amount of
 code being exercised by a set of tests. It is an indirect measure of test
 quality and completeness. This package is compatible with any testing
 methodology or framework and tracks coverage of both R code and compiled
 C/C++/FORTRAN code.