Locates event labels in text of 'ISL' results output from read_results
and their associated row numbers. The resulting data frame is joined back
into results to include event names
event_parse_ISL(text)
returns a data frame with event names and row numbers to eventually
be recombined with swimming results inside swim_parse_ISL
output from read_results
followed by
add_row_numbers
event_parse_ISL
is a helper function inside
swim_parse_ISL