updated pdf in in inst/doc
continued to work on section 3 of vignette, also realized I didn't reference the actual names of example dataframes in section 2 so I added the name of the example dataframe
Finished section 3 of the vignette--went back and edited parts of the example code
added updated .pdf of the vignette
Merge pull request #9 from schristel-USGS/master

pull changes made to vignette