Merge thunk tool into ouch tool

Merges the `thunk` tool and expands `ouch` with CLI options:

```
  ouch -e C4Cl6               # enumeration
  ouch -f some_compounds.smi  # list compounds in SMILES file
```

In general `ouch -?`:
```
  Common flags:
    -f --file=FILE          List compounds from SMILES file
    -e --enumerate=FORMULA  Enumerate molecular formula
    -? --help               Display help message
    -V --version            Print version information
```