fix: read blank lines and blank cells in CSV files

[ToddFincannonEI]

Fixes #308

I enabled 'csv-parseflags to not skip empty cells and empty rows inreadCsv`. This fixes the test case in the issue. EPS is building OK with this change.

I don't know why these flags were disabled in the first place. Vensim formulas contain absolute cell references that will be incorrect if empty rows and cells are skipped.

The test:c-int model tests run OK. I wanted to add the test in the issue to directconst.mdl, but the recent h.csv file with non-numeric cell gives a fatal error in Vensim 9.2.1, so I could not produce the reference .dat file.

[chrispcampbell]

@ToddFincannonEI:

I wanted to add the test in the issue to directconst.mdl, but the recent h.csv file with non-numeric cell gives a fatal error in Vensim 9.2.1, so I could not produce the reference .dat file.

I had left a comment in directconst.mdl regarding how to deal with the "invalid cell" test:

h[DimB, DimC] =
  GET DIRECT CONSTANTS(
    'data/h.csv',
    ',',
    'B2'
  )
  ~
  ~ This csv file has a cell that does not contain a number so that we can check that
    SDE does not throw an error in this case.  Note that Vensim will raise an error if
    a cell in the csv file does not contain a number, so to run this test in Vensim,
    temporarily change cell C3 to 0 in `h.csv`.

But I recognize that it was subtle and easy to overlook, so I moved that to its own model test (directconst_invalidcell) to avoid polluting the normal directconst test. After doing that, I took your test that was attached to the issue and folded it into the existing directconst test. So now we have test coverage for both issues.

The fix itself looks fine, so I'll merge this all shortly.

[chrispcampbell]

Looks good.