Insilicoseq

This is a bugfix release

Minor changes:
* Fixed installation problem

This release adds multiprocessing support for the read generation module 🎉

Major changes:

* Multiprocessing! `iss generate` now uses 2 cpus as a default
* change the number of cpus with `--cpus` or `-p`

Minor changes:
* somewhat updated documentation

This is a bug fix release.

Bug Fixes:
- The deletion code no longer sometimes causes an IndexError ( 21 )
- Trying to introduce sequencing errors on ambiguous bases no longer crashes the software ( 20 )

Major changes:

- The main error model switched from a simple Kernel Density Estimation to a two-dimensional Kernel Density Estimation. The new model is better at estimating the mean sequence quality and produces more realistic sequences overall
- The insert size of the generated pairs is no longer fixed but follows a more realistic distribution
- added a `--gc_bias` option to naively discard some sequences that fall outside a normal range of GC content.

Bug fixes:

- fixed a bug that would affect the substitution rate for T, G and Cs

Changes:

- New `--abundance` parameter. InSilicoSeq doesn't require an abundance file anymore and can model an abundance distribution
- New `--ncbi` parameter. You don't necessarily need input genome(s) either, they can be randomly downloaded from ncbi genomes!

Bug Fixes:
- the indel generation code now skips Ns instead of failing

This release is basically 0.2.1 without the 3 new error models