Rename examples to work with later versions of Golang (#1225)

Author: TristonianJones

examples/simple_test.go examples/example_cel_eval.goexamples/simple_test.go renamed to examples/example_cel_eval.go

@@ -21,7 +21,7 @@ import (
 	"github.com/google/cel-go/cel"
 )
 
-func ExampleSimple() {
+func Example_cel_Eval() {
 	env, err := cel.NewEnv(cel.Variable("name", cel.StringType))
 	if err != nil {
 		log.Fatalf("environment creation error: %v\n", err)

examples/custom_instance_function_test.go examples/example_cel_member_test.goexamples/custom_instance_function_test.go renamed to examples/example_cel_member_test.go

@@ -23,7 +23,7 @@ import (
 	"github.com/google/cel-go/common/types/ref"
 )
 
-func ExampleCustomInstanceFunction() {
+func Example_cel_MemberOverload() {
 	env, err := cel.NewEnv(cel.Lib(customLib{}))
 	if err != nil {
 		log.Fatalf("environment creation error: %v\n", err)

examples/custom_global_function_test.go examples/example_cel_overload_test.goexamples/custom_global_function_test.go renamed to examples/example_cel_overload_test.go

@@ -23,7 +23,7 @@ import (
 	"github.com/google/cel-go/common/types/ref"
 )
 
-func ExampleCustomGlobalFunction() {
+func Example_cel_Overload() {
 	env, err := cel.NewEnv(
 		cel.Variable("i", cel.StringType),
 		cel.Variable("you", cel.StringType),