allow umap key as feature

[AndyHoang]

I sometimes accidently do <leader>r and typing, until I realize it was changing quite a lot thing in my buffers
I can map it to another keys but I think an option to unmap key is very helpful

Thanks

[wincent]

You can unmap it. Something like this should suffice:

nmap <Nop> <Plug>(FerretAcks)