Added thrift (extension only) formula

Following up on #807 - I've replaced the thrift formula fork with extension only formula. They are quite simple yet also limited as installing the extension only provides the user with the thrift_protocol extension which accelerates the thrift binary protocol. 

The user would still require a thrift compiler and thrift library to do development work. Ideally this would be provided by homebrew itself, https://github.com/Homebrew/homebrew/blob/master/Library/Formula/thrift.rb , but that formula is broken for the foreseeable future. Yet this division of thrift and thrift-php-extensions is the only way to satisfy all parties at the moment. And hopefully get something that can be included into the official homebrew.

If anyone is interested in my original solution from #807 they can tap our repo with backports. 
```
brew tap onlinecity/backports
brew install thrift-backport --with-php --with-python
```

Doing so requires a php (5.3/5.4/5.5) from homebrew already installed, so I assume you already did something along the lines of
```
brew tap josegonzalez/php
brew install php55 
```