Update dependencies
Fix redirect test
Change File.read to cached content
Refactor of external URL checking
Allow initializer to pass Typhoeus options

Also add option to disable external link checks
Bump Typhoeus version
Move tests around
Refactor the :poop: out of everything
Execute HEAD requests, to speed up the URL checks

Hey here's a funny bug: sometimes HEAD requests return a 404, even on
legitimate pages! The
bug seems to affect curl; try `curl -I -X HEAD
https://help.github.com/changing-author-info`. So in these cases, try a
regular `GET`. If it fails, it fails.
Resume being aggressive
This slash may--or may not!--exist.
Corrections to relative root detection

Proofer now supports iterating over single files, so make sure we’re
using the file’s dirname if it’s not actually a directory
Semantic cleanup
Address comments
A little bit of cleanup
Merge pull request #24 from gjtorikian/speedup-redux

Speedup, Redux