fix tide file creation for gauges where values for variables are empty for the
period being examined (but the values exist elsewhere in the dataset)
closes #81
Merge branch 'master' of github.com:twdb/hydropick
add an option to export survey points without preimpoundment, closes #82
add notes about --export-no-pre to README
Merge pull request #85 from twdb/export-without-preimpoundment

Export without preimpoundment