Lots of bug fixes and better IO

This release mostly consists of bug fixes or enhancements to various methods from a range of contributors.

Among the new features in this release are:

• A new method DataFrame.from_activerecord to load data from Ruby on Rails.
• Better loading of SQL data and abstraction of SQL specific features to Daru::IO::SqlDataSource.
• Latest development dependencies and a few more optional run time dependencies like bloomfilter-rb.

See the History.md file for a full changelog.