modified loadCompEvent function to handle periods with only one sample and added a column in the return dataframe to indicate how many samples there were for each event.

Changed a comment in plotHydroConc
modified WQcompos to use begin and end dates and times for all samples in the final df. Also added a "codes" option to paste lab IDs together for a combined lab ID that reflects all samples included in the overall composite sample.
Merge pull request #21 from srcorsi-USGS/master

Steve's stuff.