Address issue #103 and #102

[jennwuu]

Closes #103
Identified an issue when subcatchments are named numerically (e.g. 1, 2, 3, 4), the polygon dataframe index is automatically converted to integer from string, so when coords column is assigned is not updated.

See example_1 model input.

Closes #102
Add flexibility in columns depending on swmm version number.

I add function to extract swmm version from .rpt file
https://github.com/jennwuu/swmmio/blob/cd03ae9b7cb1c7358b62e0b2d9259ab90c746f7b/swmmio/core.py#L459-L467

I add a new section in header yaml to allow more columns based on swmm version

https://github.com/jennwuu/swmmio/blob/cd03ae9b7cb1c7358b62e0b2d9259ab90c746f7b/swmmio/utils/text.py#L216-L224

swmm5_version:
  1.13:
    rpt_sections:
      Subcatchment Runoff Summary:
        - Name
        - TotalPrecip
        - TotalRunon
        - TotalEvap
        - TotalInfil
        - ImpervRunoff
        - PervRunoff
        - TotalRunoffIn
        - TotalRunoffMG
        - PeakRunoff
        - RunoffCoeff

[jennwuu]

@aerispaha, not sure why travis fails though

[aerispaha]

I like this a lot. I have a few comments and I'm going to push a couple changes momentarily. Thanks!