distance api - departure and arrival times

[SymbolixAU]

the API now says they can be in seconds since 1970-01-01

https://developers.google.com/maps/documentation/distance-matrix/intro

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Need to change parameter checks to allow positive integers as well as POSIXct objects, and check for pre-1970 times

• https://github.com/SymbolixAU/googleway/blob/master/R/parameter_checks.R#L227

• https://github.com/SymbolixAU/googleway/blob/master/R/parameter_checks.R#L307

• https://github.com/SymbolixAU/googleway/blob/master/tests/testthat/test-google_distances.R#L50

• https://github.com/SymbolixAU/googleway/blob/master/tests/testthat/test-google_directions.R#L73

[SymbolixAU]

Compares if mode == driving and departure time is in the past