Export count as a variable when running commands

[joelim-work]

Fixes #1180

This change exports the command count as the variable lf_count so that it can be used by shell scripts. For example, with the following config file, typing 123e will result in printing 123.

cmd echocount %echo "$lf_count"
map e echocount

This is similar to the v:count variable in Vimscript:

function! EchoCount()
    echo v:count
endfunction

nnoremap <silent> e :<c-u>call EchoCount()<cr>

" Typing '123e' will result in printing '123'

This feature was requested by a user, please see the discussion in #1180 for more details about their use case.

[gokcehan]

@joelim-work Oh, I didn't realize you already have a PR for this. As I mention in the discussion, this patch fixes #62 . Thanks for the patch.