Changed some severities:

>= 50% eval=FALSE vignette chunks is now a warning.
No running examples in man pages of exported examples is now a note.
Check that package NEWS is present and well-formatted.
update todos
update todos
show relevant url when warning about missing dll registration
emit NOTE with % of lines > 80 chars long
check for tabs and indentation with a non-multiple of 4 spaces
Merge branch 'master' of https://github.com/Bioconductor/BiocCheck