replace slide.content while inheriting from parent layout.
add is_installed to utils
throw error if slidifyLibraries is not installed.
remove commented out code.
add utility function %?=%
minor refactoring of code
refactor code
minor fixes to code
add in_dir function to utils.R
add blogify functions to package
export pagify and blogify
refactor code
refactor more code
use in_dir to execute render_page
move away external functions for blogify
export render_page and render_pages
remove blogify2.R from DESCRIPTION
remove pagify and blogify from exports since they have been moved.