fixed to make use of new hashed pid & also an episode start time as a fake POSIXct & a string; latest run

updated function to create uniq pid & diarypid using a hash function to ensure unique ids across all years (including UK TU 2014)

added str_epStartTime back as some diaries in 1974 do not have a known date (so dateTime is NA). str_epStartTime allows us to know what time they started as a string so they are not left out.

Merge branch 'master' of https://github.com/dataknut/MTUS

# Conflicts:
#	MTUS-W6-adult-survey-data-processing.html
#	MTUS-W6-adult-survey-data-processing.md

added time/date processing functions, only saves actual episode start/end dateTime to avoid future confusion (and makes a smaller file); latest run

added code to extract UK 2000 in raw form for reference (useful when converting other UK data to MTUS)