Stop using libraries that complicate dev setup

[compwron]

namely libv8 and therubyracer
I am setting up a new laptop and I had these troubles.

From the readme:
If during bundle install you run into errors installing libv8 or therubyracer, on Mac you can solve that with the commands below (also, see other options discussed in this gist):

# Get the version numbers from your error output. At the time of this writing, I used:
# libv8: '3.16.14.19'
# therubyracer: '0.12.3'
$ brew install v8@3.15
$ gem install libv8 -v 'YOUR_VERSION' -- --with-system-v8
$ gem install therubyracer -v 'YOUR_VERSION' -- --with-v8-dir=$(brew --prefix v8@3.15)
$ bundle install

We should also move away from gem thin if possible because it has a similar error on osx without xcode installed, solvable by macournoyer/thin#365 gem install thin -v '1.6.4' -- --with-cflags="-Wno-error=implicit-function-declaration" or similar.