slugify section headers
slugify section headers

The current section headers are url encoded.  Because of that they
have some funny characters like %20.  We can clean that up by removing
all of the non-word characters before placing them in the anchor.

superstring/mdBook,azerupi/mdBook,petehayes102/mdBook,superstring/mdBook,petehayes102/mdBook,azerupi/mdBook,superstring/mdBook,petehayes102/mdBook,azerupi/mdBook,azerupi/mdBook,superstring/mdBook,petehayes102/mdBook