Merge pull request #2 from jefferis/master

thanks. close #2
make check and TOC
make view
h2 is better, packrat frozen (look ctv)
added CONTRIBUTING
pandoc README.md
is it published on the repo page, now? mmm let's see
link fixing target
link fixed
TODO added
pkg added within comments
make aspell; make aspell-make-dict
better target naming (aspell-dict)
html making fails with missing packages, now
make check-links
added sed preprocessing: <gh>hadley/devtools</gh> allowed, section and task auto-formatting
after sed preprocessing
Package Doc fix
task better names
again