[rake-scaffolding] 'slides/' is our working directory

* New task: rake presentation
 * This is the default task
 * It copies in the core of the slides, slides.html, into slides/
 * It copies in all of reveal.js (git submodule) into slides/

Next up: slice up slides/index.html so that the default reveal stuff
is no longer present.
[rspec] spec_dir: a method that returns absolute path of spec/
[file-slicer] FileSlicer: Failing test

* Creates a tmp directory
* Copies in a file to be 'sliced' (data/*/before_slicer)
* Slices the file in the tmp directory
* Compares sliced up file to expected output (data/*/after_slicer)
[file-slicer] FileSlicer: It removes a numeric range of lines from a file
Merge branch 'file-slicer' into rake-scaffolding
[rake-scaffolding] Remove default reveal-js content with FileSlicer

* Now part of ```rake presentation```