Can I have multiple configs for a same tool?

Config:
```javascript
let g:grepper = {
\ 'grep': {
\ 'grepprg': 'grep -Rn $* .'
\ },
\ 'grepI': {
\ 'grepprg': 'grep -Rni $* .'
\ },
\ 'grepFile': {
\ 'grepprg': 'grep -Rni $* $.'
\ },
\ 'tools': ['grep', 'grepI', 'grepFile']
\}
```
Then in vim:
to grep case-sensetive
```bash
:Grepper -tool grep -quickfix -highlight
```
to grep case-insensetive
```bash
:Grepper -tool grepI -quickfix -highlight
```

Start with the plugin's handling of the g:grepper configuration and the :Grepper -tool command, using the shown grep, grepI, and grepFile definitions as examples. Determine whether multiple configurations can be selected independently; done means the commands use their respective grepprg settings.

Written by the indexing model from the issue text.