Ps merging annotating genecounts

[preetisi]

This branch generates annotations.txt file (its a tab separated file). I have validated the results with altanalyze2 annotations file (counts.test.txt). The improvements that need to made here:

1. Index the junction files, I have added some code for indexing the files, it's in utilities folder. But Misha might have to change it as it needs to be OS agnostic.
2. Add multiprocessing step.

Then these results can be used to make h5ad format file.