CT: CT-40 exit numbers

[rickmastfan67]

I-91 -> 1A or 1B or 1C, pick your poison.

This is due to the US-5 exit being posted as '1' going NB, however, it's posted as '1D' going SB.

[yakra]

I-91 -> 1A or 1B or 1C, pick your poison.

1A. It's the lower letter, and there is another interchange with the same number and different letters.
The latter rule could also lead to it being plain 1, but that's in use at the next interchange.

This is due to the US-5 exit being posted as '1' going NB, however, it's posted as '1D' going SB.

Leaving this as 1 also works, but I've changed it to 1D, per the usually keep the letter rule.
This better differentiates it from 1A et al, and maintains alphanumeric order as the route goes northward.

https://github.com/TravelMapping/HighwayData/commit/5b76d4fc18ac5fa114149add84b49bd4c8d092ce