Check if the "lime" command is installed

[Gama11]

Right now, the extension just fails silently if that's not the case. It should show a helpful error to the user so he knows what's going on.

[ibilon]

Just had that issue

> Executing task: lime build neko <
/bin/bash: lime: command not found
The terminal process terminated with exit code: 127

I only have a bash alias for convenience but not the command. Lime (and all haxelibs) is installed in my home directory so adding a global executable doesn't make sense.

Could the extension run haxelib run lime instead? It's a lot more likely to succeed.

[Gama11]

Closed by #36. You can now add this to your settings:

"lime.command": "haxelib run lime"