Change data frame names for climate object

[jarad]

Currently read_cli() returns a data.frame named precip, but this data frame has other weather variables and no precipitation. The nbrkpt contains the precipitation information sub-daily. A proposal is to rename precip to weather and add a column for total daily precipitation. Also, we could rename nbrkpt to precipitation. We could also remove nbrkpt column from the current precip data.frame.

But, before we make these changes we should look at what the WEPP user summary says.