Remove Numeric Prefix from Files

[ericpassmore]

Removing the numbers the lead the file and directory names is a good idea. The numeric prefix is used to order the contents on the sidebar. This repository switched methods to use the meta-data embedded inside the markdown files to drive sidebar order. It's confusing to mix/match the ordering, and it may lead to an undefined state, and different methods complete for order.

Recommend first making this change on a subset of files and testing for broken links.

[nsjames]

File numbering is preferable as you can see the ordering at a glance from the file structure instead of having to either load up the site or go through each file.