Included optional run for createRules script.

[a-t-0]

Hi, thank you for sharing this body of work with the world!

Issue

I experienced some difficulties in auto-generating the .rules file for a specific bank with the preprocess script, as that script requires the .rules file to already exist. And I experienced some difficulties using your software to convert the 2-preprocess files into 3-journal files with the construct script, as that is assumed to do that itself.

Solution

So I modified CSVImport.hs to run a createRules script if it exists prior to running the preprocess script.

Limitations

The function call with the call towards the createRules script is added under the preprocessIfNeeded function, which makes the preprocessIfNeeded function do 2 things instead of one. So it would be better to refactor that, however I never used Haskal and had limited time allocated to this solution, so I hope you feel free to reject the PR or specify exact requirements for acceptance if you would like the functionality to be included.