Remove unnecessary conditional assignments

`smells_before` and `smells_now` are always arrays anyway.
Extract report location to its own method
Remove unnecessary `require`s
Always output the report in the same file when using Guard

This way, all a user has to do is refresh the browser to get the current
file analysis.
Shell-escape committed files' names

A file named something like `''; echo MALICIOUS ATTACK 1>&2;.rb` could
have easily owned us.

For more information on using the shell in Ruby, check out [Shelling Out
Sucks][1].

[1]: http://julialang.org/blog/2012/03/shelling-out-sucks/