add a Developer_Style_Guide.Rmd vignette

[jonathancallahan]

For anyone in the future who might want to modify or enhance the code in this package, it will be useful to have a good understanding of how and why things are named as they are. To support consistency, we should provide a style guide for developers.

Please copy the following file to the vignettes/ directory and modify it as needed to reflect the "objects" and functions in the RAWSmet package:

https://github.com/MazamaScience/MazamaSpatialUtils/blob/master/vignettes/Developer_Style_Guide.Rmd