write_inp_section changes - don't change the Polygons header

[BuczynskiRafal]

Closes #181

[BuczynskiRafal]

@aerispaha I'm not sure how to test the solution. Can I find a method in swmmio that reads the header in the inp file to compare it with the header after doing replace_inp_section?

[bemcdonnell]

@BuczynskiRafal, I'm guessing you're adding this feature because of some kind of text version control issue. I think the best way to test it is to add a second INP file with [POLYGONS] and check the outputs from that. You can use a simple file parser to assert that the text found is either your [Polygons] or [POLYGONS]

[BuczynskiRafal]

@aerispaha @bemcdonnell Please review my PR. Thank you.

[aerispaha]

@BuczynskiRafal thanks for this great contribution to swmmio! Overall, your bug fix seems to work great.

My only request is that we remove the new swmmio/tests/data/example_polygons.inp file from this PR, and use a test inp file that already exists in the repo. I'd also suggest we refactor the unit test as I described below for a couple reasons:

1. this way test files aren't left behind if this test fails
2. I'd prefer to emphasize the model.inp.<section> = <dataframe> pattern for updating models, rather than using the replace_inp_section function directly.

Let me know what you think!

[BuczynskiRafal]

@aerispaha Thanks for the good points. I've made the changes.

[aerispaha]

This looks great, @BuczynskiRafal! I'll get this integrated into the next release asap