Cleaning the repository

These 2 commits remove some unused things from the repo and also update the README file, something very important if we want to grab the attention of new contributors.

There are many, many other changes that could be useful, e.g. clean the Rakefile, remove stuff from the Gemfile (that's why we have gemspec!) and, obviously, update the code and specs. As I need to work on the GSoC application, I won't be able to do all this today.

One thing at a time.

[5dbfc8](https://github.com/agarie/sciruby/commit/5dbfc81683fad3a743035e43309bf717aa9dda5f)

The code being tested in test/ is deprecated, old and unmaintained. We should
clean this mess before inviting people to contribute to SciRuby.

The static/ directory contained only a logo, which I will send as a PR to the
sciruby.com source branch.

And, finally, I removed some things from the gemspec -- too many things there.

[8cd19a](https://github.com/agarie/sciruby/commit/8cd19a4eb5741f2ade6e940a6cf3b2af14b1259a):

I made changes to the README similar to those made in NMatrix's:

- Re-arranged the headers (all in lowercase).
- Put all the information regarding developers in CONTRIBUTING.md (so it'll
appear when someone opens a pull request).
- Fixed link to the pledgie image.
- Improved link names and descriptions.
- Added link to installation page on the wiki.
- Warned about NMatrix/rb-gsl incompatibility.

Also, explained a little bit about how SciRuby and its subprojects are related
in the CONTRIBUTING.md file.