Move shims into their own directory

With three shims now it makes sense to move them to their own dedicated
directory.

.busted

@@ -26,7 +26,7 @@
 return {
 	_all = {
 		coverage = false,
-		lua = './test/lua',
+		lua = './test/bin/lua',
 		['exclude-tags'] = {'skip'},
 	},
 	default = {

makefile

@@ -28,13 +28,13 @@
 check: unit-test e2e-test highlight-test
 
 unit-test:
-	@./test/busted --run unit
+	@./test/bin/busted --run unit
 
 e2e-test:
-	@./test/busted --run e2e
+	@./test/bin/busted --run e2e
 
 highlight-test:
-	@./test/busted --run highlight
+	@./test/bin/busted --run highlight
 
 clean:
 	@rm -rf test/xdg/local/state/nvim/*