hurdle method fully implemented please review

[statOmics]

I implemented the hurdle method based on forked Features 0.6.1. at the lgatto repository.
It makes use of novel the .n and the aggressive counts ;-) functionalities.
The hurdle vignette is also updated accordingly.

[ococrook]

Hi @statOmics,

Looks good to me - I made a number of edits to the vignette. I also tidied up the code but didn't make any large changes.

See recent pull request