openintro 2.0.0

• Added a NEWS.md file to track changes to the package.
• Consolidated openintro, oilabs, and oidata packages.
• Updated all dataframe and variable names to use snake_case.
• Turned data.frames into tibbles.
• Simplified code in most examples to make it more accessible for the student audience for the package.
• Added new datasets used in OpenIntro Statistics, 4th Edition.
• Added new datasets used in new OpenIntro labs.
• Removed package startup message.
• Added dependency on the following packages: airports, cherryblossom, and usdata.
• Moved run09, run12, and run19 datasets to the cherryblossom package.
• Moved usairports to the airports packages.
• Moved county_complete, county, govrace10, houserace10, prrace08, senaterace10, state_stats, urban_owner, urban_rural_pop, vote_nsa datasets and state2abbr and abbr2state functions to the usdata package.