Add support for ".txm" format
Neat! Looks like you need a rebase and then should be good to go :)  Done, @yjernite, @lhoestq. If you agree, we could merge this. Hi ! yes sure :) can you just merge master into this branch before we merge ? Done @lhoestq 
In dummy data generation, add support for XML-like ".txm" file format.

Also support filenames with additional compression extension: ".txm.gz".