Fix ubuntu installation and remove monkey-path

This commit has fixed the `cannot load such file -- summarize/summarize` error. This error occurs when we build the gem spec `gem build summarize.gemspec` using ubuntu. These behaviors do not occur on Mac. After some investigation, we discovered that `summarize.so` was being built in `./lib/summarize.so`. To Fix it we needed to create the folder `./lib/summarize`, them `summarize.so` was created in `./lib/summarize/summarize.so`.

As we needed to create the `./lib/summarize` folder, we decided to move LANGUAGES and VERSION to the new folder.

After all that done, we fixed the need of monkey-path, now the user can choose to opt-in the monkey-path by ```require 'summarize/core_ext'``` otherwise he will use ```Sumarize.summarize('text to be summarized')``` with the same params as the monkey-patched method.