Rename "Stage II" directory as puf_stage2

[martinholmer]

This pull request eliminates the space in the directory name and switches from Roman to Arabic numerals. Also, the CLP_solver_16Years.py script has been renamed stage2.py and that script has been reformatted (hopefully without any substantive changes) to eliminate PEP8 warnings. And the Single_Year_Stage_II.py script has been renamed solve_lp_for_year.py and that script has been reformatted (hopefully without any substantive changes) to eliminate PEP8 warnings. And finally, a copy of the WEIGHTS.csv file from the Tax-Calculator repo has been added to the directory as the puf_weights.csv file.

I don't have the LP libraries installed on my computer, so, @andersonfrailey, you are going to have to test the new code to see if it still produces the puf_weights.csv file. Let me know if you need a little bash script that downloads this PR and opens it as a new taxdata branch on your computer.

As I write up this pull request, I see that I have misnamed the new directory: it should be puf_stage2 and not simply stage2. Let's do the testing and when we pass the test we will merge the current PR. Then in a subsequent PR I'll correct the directory name.

[andersonfrailey]

@martinholmer can you give me the bash script to download and open this PR locally? I haven't had any luck googling it.

[martinholmer]

I have renamed the stage2 directory as puf_stage2 and installed the cylp package on my computer. So, I am now able to test pull request #63 on my computer.

[martinholmer]

Using PR #64 code, the puf_stage2/stage2.py script generates exactly the same puf_weights.csv as produced by earlier versions of taxdata.