Getting ready for CRAN

[ldecicco-USGS]

• Added read_waterdata_latest_daily to access latest daily USGS water data.
• Added read_waterdata_continuous to access continuous USGS water data.
• Added state_name and hydrologic_unit_code to read_waterdata_ts_meta
• Removed daily_id from read_waterdata_daily output since it
  is not stable over time. Moved other "id" columns to end of returned data frames.
• Changed examples for stateCd, countyCd, and parameterCdFile. Users are
  encouraged to migrate to the "read_waterdata_metadata" functions.
• Added no_paging argument. This will make the request more efficient, but is not
  recommended because it will silently cut off data after 50,000 rows.
• Removed max_results argument. Was confusing and redundant with the combination
  of no_paging and limit.
• Increase the flexibility of read_waterdata_metadata to match other OGC functions.
• NLDI to use agency code prefixes and should no longer be stripping the "USGS-" off the site ides.
• Add deprecate message to readNWISuse function as data services have been retired.