Convert SAS scripts to R or Python

[nmpeterson]

Currently, most of the MHN processing tools rely on one or more SAS scripts. In the interest of making the code useful to as many people as possible (and, frankly, to get away from the awful SAS language itself), those scripts should be converted to a language that can be interpreted by common, free software -- either R or pure Python, depending on the script.

Of course, all of the scripts still require an ArcGIS license...

[nmpeterson]

generate_transit_files_3.sas has been rewritten in Python -- the generate_rail_pnt_files() function in generate_transit_files.py -- see #54. (generate_transit_file_4.sas was subsequently renamed _3 -- #55.)

[nmpeterson]

update_highway_project_years_2.sas has been rewritten in Python -- the clear_transit_project_years() and get_trans_proj_scens() functions in update_highway_project_years.py duplicate the functionality of the old SAS script. See #58.

[nmpeterson]

If for any reason this effort is abandoned, there is now a Python package called "SASPy" -- developed by SAS for smoother python integration, which may be worth looking into.