New function extract.units() to get measurment units of all channels from parsed header.
Helper function first().
extract.units() now returns a dataframe of parameter names and units.
Bugfix in extract.units(): typo (x in place of u).
extract.units() understands more synonyms for "water level" that occur. More typo bugfixes.
read.mon.complete() converts water level data to metres based on parameter "unit".  Limit for "out.of.water" functions is in metres.
Collect synonyms for "water level".