show how to retrieve list of options and engines
also show default package options in the docs
don't build manual for Travis tests (necessary because now the Rd files contain \Sexpr-s)
show lines in which Sweave syntax has been encountered
detect T and F in addition to TRUE and FALSE when converting Sweave syntax
Merge pull request #674 from krlmlr/default-opts

Docs for default options
Merge pull request #676 from krlmlr/675-Sweave

show lines in which Sweave syntax has been encountered
roxygenize
cosmetic
news for #676