Enormous amount of modifications.

I updated the README with more information about what I wish for this project.

As I decided to employ pure Ruby implementations while I decide how the API
will work, the ext/ directory and everything related to C extensions was
removed: rake tasks, gemspec statements, code, specs.

I added more distance measures to the ones I want to support, but for now, they
still need to be implemented.

The version was bumped to 0.0.3 because too many changes were made. Besides, I
will probably release a 0.1.0 version without C extensions, so it's not like it
will be too difficult.

I *still* need to finish writing specs for everything.

Ah! And I need to implement the max-min distance.