shorten url's of manuals, and add citation('knitr')
use do.call('render_foo') instead of explictily listing all render_foo functions

also need to add render_brew() for the brew output
change the rules for the output name a little bit:

- if input contains _knit_, remove it
- if extension is not txt, use .txt
- otherwise use foo-out.ext

also need to update the tests
add asciidoc in the output format (#510)
how did I forget to add (.*) to chunk.begin??
image captions start with a period .
change the inline syntax to +r + instead of `r ` to avoid confusion with markdown
remove the inline hook in asciidoc; just use the default hook -- users may not want ++
clean up messages for asciidoc
news for asciidoc
roxygenize
bump version