Support Sequel ORM

[cmrd-senya]

No description provided.

[zealot128]

hello. Thanks for your PR. Would you mind adding a test that demonstrates the usage?
Also an entry to README would be nice, that explains usage.

[cmrd-senya]

Would you mind adding a test that demonstrates the usage?

I wouldn't mind, but I think you should accept #64 first, in order to avoid conflicts here.

[cmrd-senya]

simple-captcha2 uses Rails generators to create a dummy application to test the gem against.

I added support for generating a Sequel based Rails application. It is activated by setting SEQUEL env. I added respective scenario to the travis configuration.

ORM is meant to be selected automatically, so in terms of usage it doesn't require any explicit user actions, except of including proper gems to user's Gemfile. I added a little note about this to the readme. (Note: this is not my idea, there was a support for ActiveRecord/Mongoid selection before my work).

[cmrd-senya]

Just in case I'll say that this is ready for a review