CRAN re-submit

[mpadge]

Got kicked off because of #111. Have to re-instate it.

[mpadge]

CRAN email 14/9/23:

Please add \value to .Rd files regarding exported methods and explain the functions results in the documentation. Please write about the structure of the output (class) and also what the output means. (If a function does not return a value, please document that too, e.g. \value{No return value, called for side effects} or similar)
Missing Rd-tags:
gtfs_traveltimes.Rd: \value
process_gtfs_local.Rd: \value
summary.gtfs.Rd: \value

Please always make sure to reset to user's options(), working directory or par() after you changed it in examples and vignettes and demos. ->
e.g.:
oldpar <- par(mfrow = c(1,2))
...
par(oldpar)

Please fix and resubmit.

[mpadge]

Possibly misspelled words in DESCRIPTION:
GTFS (2:21, 10:18)
isochrones (12:5)

Examples with CPU time > 2.5 times elapsed time
user system elapsed ratio
gtfs_route 1.223 0.037 0.38 3.316