using mosdepth with a small RAM
I am working on a cloud machine with 1GB RAM and mosdepth is throwing OOM error. Is there a way I can tell mosdepth to be parismonious?

```python
[
	'export MOSDEPTH_Q0=NO_COVERAGE &&',
	'export MOSDEPTH_Q1=LOW_COVERAGE &&',
	'export MOSDEPTH_Q2=CALLABLE &&',
	'mosdepth',
	'-x -n -t 1',
	'-q 0:100:1000:',
	prefix,
	input_fn,
],
```