Upcoming commands

Since we are going to be doing a refactor of the CLI anyways, it maybe worthwhile to think about what commands to have.

Right now, we have
```
rhapsody mmvec --help
```

Which is ok if mmvec is the only command - however in the near future, we'll be adding in multiple additional commands, namely

`seq2seq`: to explicitly handle sequence count inputs and sequence count output (which is the default now). May want to add overdispersion later
`seq2spectra`: to handle count inputs and continuous (lognormal) outputs

If we go this route, it also makes sense to ditch the wrapper name and call this whole package mmvec. So this would now look like

```
mmvec seq2seq --help
mmvec seq2spectra --help
```