Fix bug in project makefile substitution
Move knitr utils into separate file knitr.R
Move knitr utils into separate file knitr.R (2)
Update man page for alphacol
Add toggle code feature and backspace handling as a knitr extension
Update knitr extension man page and NAMESPACE
Fix issues in str_bs, add knitr hook_toggle and update man pages with clearer separation between examples
Bump version to 0.18 and update vignettes
Merge branch 'release/0.18'