metro 0.9.1

This is the initial beta release of metro. Almost all JSON endpoints in the WMATA API are covered as functions returning a data frame of transit data. The functions are still experimental and the structure, names, and types of columns may change prior to the 1.0.0 release. Some endpoints (like rail station parking) still need to be thought about more before a proper data frame version can be implemented.

• 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.