* Updated getSiteFileData to retrieve multiple site file datasets at once using a vector of siteNumbers as input argument.
* Updated error-handling for Web service calls. More information is returned when errors happen
* Added some basic processing to Water Quality Portal raw data retrievals. Date columns are returned as Date objects, value columns are numeric, and a column is created from the date/time/timezone columns that is POSIXct.
* Added very generalized NWIS and WQP retrieval functions (getNWISData, getNWISSites, getGeneralWQPData, and getWQPSites) which allow the user to use any argument available on the Web service platform.
