Add support for blocking reads

[joshmyzie2]

To use a haskell application as a subscriber to a kdb+ ticker plant, it's necessary to have a blocking read function. I've added a simple readKdb function here:

https://gist.github.com/joshmyzie2/7804c53be8ea5942f364

[jkozlowski]

Hey,

I will sit down next weekend and fix the build and apply all these PRs finally. Would you like to send a proper PR and add some tests for this?