Remove publication_date attribute from Experience model.

Removes the publication_date attribute from the Experience model. I
don't want this functionality anymore so I am removing it from the
codebase.
Update README.

Updates the README with some extra text.
Add RSpec skeleton.

Adds RSpec skeleton and sets the output format to documentation to take
a quick glance at what does which method.
Add Guard gem.

Adds the Guard gem to automate RSpec specs runs.
Add database_cleaner gem.

Adds the database_cleaner gem to ensure clean state for testing.
Add factory_girl gem.

Adds the factory_girl gem for Rails (actually, factory_girl_rails) as a
fixture replacement that might speed up test running times.
[fix] Remove unnecessary require from RSpec support file.
Add first spec for Experience.

This commit has emotional value only. I want to do this right. I will
keep testing properly only to get to the highest condition of testing expertise.