soft-masked bases

Hi there, in the README it says that krust aims to give the same output as jellyfish. However, jellyfish counts softmasked bases, whereas krust does not. Is this intended?

See below for example:
```bash
$ cat bla.fa 
>seq
AAAa

$ krust 3 bla.fa
k-length: 3
data: bla.fa
reader: rust-bio

>1
AAA

$ jellyfish count -m 3 -s 100M -C -t1 bla.fa && jellyfish dump mer_counts.jf 
>2
AAA
```