Add build tags to make the project compatible with gopls (#470)

The gopls deamon for text editor integrations used to complain about the `main()` function being redeclared across multiple `package main` files that share the same directory. This is because these individual scripts were meant to be run with `go run path/to/file.go` instead of being built as a binary. The latest gopls release supports recognizing files that are meant as individual runnable scripts, but they must be tagged with a build tag that makes them otherwise ignored.

Author: mislav

examples/countrylist.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/cursor.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/inputfilesuggestion.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/longlist.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/longmulti.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/longmultikeepfilter.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/map.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/password.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/select_description.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (

examples/simple.go

@@ -1,3 +1,5 @@
+//go:build ignore
+
 package main
 
 import (