Made some changes to grid_to_line_intersection output

Made some changes to grid_to_line_intersection, changed output format to dataframe for stats, and changes stats to calculate stats on line per each date, output format of points is geodataframe and stats is a dataframe.

@Anders - please take a look. Mostly these changes just change the output formatting. Please take a look. I haven't looked at the buffered line code yet. I've attached the code I used for running the code and testing. Can you please rework your demo notebook and update your plotting function to work with the reformatted output. Also let's work with the existing ODAPCatData user data function. I'll work in Gene's new code for Mike's new Climate-R catalog later this coming week. Also because I reformated the stats output, some of the tests are failing. The stats now run stats on each of the dates the data are mapped from, so the mean for example, gives the mean of all the line-interpolated data for that date, previously they had been calculating the mean of each point for all the dates. I think this new way makes sense - do you agree? I'll be out M,T this week but back to work Wed (FYI). linecheck_2.py