Evaluate the options to autodetect the keyboard layout of the user

[pacha]

The idea is that the user doesn't have to set g:vem_layout manually in their vemrc file, and the correct layout will be taken from the system configuration.
Potential problems:

• Making it work across platforms
• Requiring external commands that may or may not be present on the system
• Figure out what to do in the case of remote editing (eg. through SSH)

@mirsella opened #3 with working code for Linux. In order to include this functionality, we should ensure that it works for (Linux, Mac and Windows or that there's a reasonable fallback).

[mirsella]

i've done this, maybe it can help someone.

if !exists("g:os")
  if has("win64") || has("win32") || has("win16")
    let g:os = "Windows"
  else
    let g:os = substitute(system('uname'), '\n', '', '')
  endif
endif

if g:os == "Darwin"
  let g:vem_layout = system('do shell script "defaults read ~/Library/Preferences/com.apple.HIToolbox.plist AppleSelectedInputSources | egrep -w "KeyboardLayout Name" | sed -E "s/^.+ = \"?([^\"]+)\"?;$/\\1/""')
elseif g:os == "Linux"
  let g:vem_layout = system('setxkbmap -query 2> /dev/null | grep -o -E "(querty|quertz|azerty)$" || echo "querty"')[:-2]
elseif g:os == "Windows"
  " windows
endif

however i'm stopping here, i don't have a mac to test the command output (it probably don't work i don't even know what i return) and i tried doing some things with windows but it's just a pain i could not even get a keyboard layout to print on cmd.

[pacha]

Hi @mirsella. Thanks a lot for the contribution! I'll try to give it a try myself in Mac and Windows when I find time. As last resort we can still add the code to the docs so people can still use it until we find a good way to ensure that it works well across platforms and different versions of those platforms.