Polygons / POLYGONS inp section is causing parsing issues

[aerispaha]

The polygons section of the INP file is special because it is sometimes called [Polygons], not following the typical header syntax with all caps i.e. [POLYGONS].

This seems to be causing issues as we try to add coverage for new INP sections (e.g. in #242). This needs to be resolved.

[dickinsonre]

Is this not a bug in SWMM5 - it seems to be the only section not uppercase

// Export vertex coordinates of subcatchment polygons
S.Add('[Polygons]');

[aerispaha]

@dickinsonre I think you're right. I suppose we could try and fix that bug in SWMM, but I think swmmio will need to deal with this for the foreseeable future either way.