feat: DSC changes

[mshodge]

Changes from the Data Science Campus, including:

• refactoring code, e.g. paste0
• including more API parameters (defaults given too)
• original otpTripTime function gives next available trip even if it’s several hours away, to avoid this we include a new parameter called preWaitTime (default 60 minutes). No result is given if start of journey is more than the preWaitTime from the desired start time. This is important for journeys using transit data, when considering accessibility over time. This should be implemented into other functions too in the future (i.e. the isochrone function).
• otpTripTime function outputs now include detailed trip table and a poly line file that can be used in leaflet (note: this is from point to point and does not follow road layouts).
• otpChloropleth included as a light version of the otpTripTime function so multiple origins to destinations can be called faster than using the modified otpTripTime function.
• otpIsochrone functions cutoff parameter altered so that an array can be passed in of any length and the result returned. This prevents limiting cutoffs to a specific number.

We have tested this on our own unit tests and each function passed:

	file	test	nb	failed	skipped	error	warning	user	system	real
1	test_GTFS.R	Test GTFS	1	0	FALSE	FALSE	0	0.181	0.021	0.756
2	test_otpChoropleth.R	Test otpChoropleth	1	0	FALSE	FALSE	0	0.080	0.005	0.213
3	test_otpConnect.R	Test otpConnect	1	0	FALSE	FALSE	0	0.001	0.000	0.002
4	test_otpIsochrone.R	Test otpIsochrone	1	0	FALSE	FALSE	0	2.202	0.181	8.984
5	test_otpTripDistance.R	Test otpTripDistance	1	0	FALSE	FALSE	0	0.024	0.000	0.085
6	test_otpTripTime.R	Test otpTriptime	1	0	FALSE	FALSE	0	0.017	0.000	0.095

These changes were made to develop a series of R scripts for certain tasks required at the Data Science Campus. If the changes are not passable (rejected) please allow us to use your original code with acknowledgements. If the changes are accepted, we will import the package into our work (again, with acknowledgements).

[marcusyoung]

@mshodge Thanks very much for the pull request and interest in the project. Because your changes are on the old R script that I originally wrote for my research, I won't accept the pull request. We now have functions being written within the R package structure. There should be a commit fairly soon with a range of those functions (including, for example, one that also returns route geometry). What I will do is review the work you have done and incorporate your suggestions into the relevant functions as appropriate. I have no problem with you using my original code in the meantime. Once again, thanks for the useful input.