Move code into a Bundler style gem package

[scottharvey]

This PR moves all the existing Repetition code into a more standard gem structure.

I did this by running bundler gem repetition and then moving the code into the generated code. This has the added advantage of making specs easier to run by calling bundler exec rake

I've also updated the README to include an example Rails migration and information on how to run the specs.

Finally I've updated an error message in lib/repetition.rb which incorrectly stated you could pass a value of 0 into .process_recall_result

[dankimio]

Thank you for the pull request!

[scottharvey]

@dankimio Are you using this gem anywhere? I've got a couple ideas how to change it but I'm not sure if I should keep creating PRs or just maintain my own fork.

[dankimio]

I'm open to new ideas! What are the changes that you want to make?

[scottharvey]

I would like to remove reset_spaced_repetition_data and instead initialize the attributes inside process_recall_result when needed.

Also, I want to be able to pass a date into process_recall_result so I can specify a date other than Date.today

Finally, I found a bug which meant repetition_interval wasn't being initialized properly in a certain case which was causing an error.

I can create a PR for each one if you are interested.

[dankimio]

Sounds like it's more reasonable to move the whole module into a separate class. What do you think? Using the gem as a mixin adds a lot of constraints and probably was not a good idea.

So it would look like the following:

# Initialize
options = { easiness_factor: 2.5, schedule_from: Date.today, ... }
flashcard = Repetition::Flashcard.new(options)

# Result (recall result is calculated under the hood)
flashcard.next_repetition # => Date

Thus, it would be possible to initialize attributes in class initializer and we can include other options, such as date override as well.

PRs for bugs are always welcome!

[scottharvey]

Yeah, it might be nice to have it as a stand alone class so it's nice a clean. But then you could could also have some extra railties code so it fits in nicely with Rails / Active Record.