Schema transformations and built-in Checks

Release Notes

Major Enhancements

• Schema transformations to add/remove columns from a dataframe schema dcc40f4
• Add built-in checks for common data validation tasks 1be3bcc
• Add dtype property to DataFrameSchema and SeriesSchema objects 7aecf16

Codebase Improvements

• update documentation
• improvements to CI 0a28e30
• improvements to linting, code quality checks cb39fd0
• clean up Check and SeriesSchemaBase internals 7bf2fe8
• add airspeed velocity benchmarks ee21cdb

Bugfixes

• • fix coercion logic for string and object dtypes df364f1, 7f572fc