metro 0.9.1

• Covered most JSON endpoints as tidy data frames. Buses stops, train stations, next bus or trains, incidents, paths, routes, circuits. (#1)
• httr::RETRY() in wmata_api() does not retry on 401, 404, etc. The purpose of this change is to primarily retry on 429 errors when too many requests have been made on a rate-limited subscription. Waiting should successfully retry.
• Stops, Stations, Routes, and Lines saved as exported objects.
• All functions accept api_key argument. (#5)
• Calls are made using httr::RETRY() to deal with issues like rate limit. (#8)
• Use the documentation and parameters in the official API documentation. (#7)
• Convert all dates to POSIXct with UTC time zone.
• Convert times to hms columns with values past midnight. (#6)
• Removed parking_*() functions until a data frames can be made.
• Removed rail_path() helper function. Keep only endpoint functions.
• Removed ability to automatically scrape demo API key.
• Removed package startup message about API key. (#2)
• Invalid URLs are removed from function documentation.