Added fancy stx_query() function

[hreinwald]

Hi Andreas, I have added the stx_query() function and adopted it to the new data table style. Further i have added some example code in the R/ repo. This does not need to be merged but might be helpful when writing some documentation for the function and the readme.

Open points

• Need to add some documentation in R code for the stx_query() function.

[hreinwald]

Somehow my pull_request failed

[hreinwald]

For some reason I keep getting pull_request failing messages. I will close this pull request now and try to re-fork the main repo again, then apply the changes and re-start my pull request.