Fixing #117 requires a change in Cmder.

So, for best compatibility, clink-completions will have both .init.lua and
!init.lua files.

!init.lua

@@ -1,3 +1,9 @@
--- The line below extends package.path with modules
--- directory to allow to require them
-package.path = debug.getinfo(1, "S").source:match[[^@?(.*[\/])[^\/]-$]] .."modules/?.lua;".. package.path
+-- Extend package.path with modules directory, if not already present, to allow
+-- using require() with them.
+--
+-- Note: This happens in both .init.lua and !init.lua because older Cmder
+-- versions don't know about !init.lua.
+local modules_path = debug.getinfo(1, "S").source:match[[^@?(.*[\/])[^\/]-$]] .."modules/?.lua"
+if not package.path:find(modules_path, 1, true--[[plain]]) then
+    package.path = modules_path..";"..package.path
+end

.init.lua

@@ -0,0 +1,9 @@
+-- Extend package.path with modules directory, if not already present, to allow
+-- using require() with them.
+--
+-- Note: This happens in both .init.lua and !init.lua because older Cmder
+-- versions don't know about !init.lua.
+local modules_path = debug.getinfo(1, "S").source:match[[^@?(.*[\/])[^\/]-$]] .."modules/?.lua"
+if not package.path:find(modules_path, 1, true--[[plain]]) then
+    package.path = modules_path..";"..package.path
+end