Move timeutils functions to the only places where they are used.

- Move time json marshaling to the jsonlog package: this is a docker
  internal hack that we should not promote as a library.
- Move Timestamp encoding/decoding functions to the API types: This is
  only used there. It could be a standalone library but I don't this
it's worth having a separated repo for this. It could introduce more
complexity than it solves.

Signed-off-by: David Calavera <david.calavera@gmail.com>

jsonlog/time_marshalling_test.go

@@ -0,0 +1,47 @@
+package jsonlog
+
+import (
+	"testing"
+	"time"
+)
+
+// Testing to ensure 'year' fields is between 0 and 9999
+func TestFastTimeMarshalJSONWithInvalidDate(t *testing.T) {
+	aTime := time.Date(-1, 1, 1, 0, 0, 0, 0, time.Local)
+	json, err := FastTimeMarshalJSON(aTime)
+	if err == nil {
+		t.Fatalf("FastTimeMarshalJSON should throw an error, but was '%v'", json)
+	}
+	anotherTime := time.Date(10000, 1, 1, 0, 0, 0, 0, time.Local)
+	json, err = FastTimeMarshalJSON(anotherTime)
+	if err == nil {
+		t.Fatalf("FastTimeMarshalJSON should throw an error, but was '%v'", json)
+	}
+
+}
+
+func TestFastTimeMarshalJSON(t *testing.T) {
+	aTime := time.Date(2015, 5, 29, 11, 1, 2, 3, time.UTC)
+	json, err := FastTimeMarshalJSON(aTime)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := "\"2015-05-29T11:01:02.000000003Z\""
+	if json != expected {
+		t.Fatalf("Expected %v, got %v", expected, json)
+	}
+
+	location, err := time.LoadLocation("Europe/Paris")
+	if err != nil {
+		t.Fatal(err)
+	}
+	aTime = time.Date(2015, 5, 29, 11, 1, 2, 3, location)
+	json, err = FastTimeMarshalJSON(aTime)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected = "\"2015-05-29T11:01:02.000000003+02:00\""
+	if json != expected {
+		t.Fatalf("Expected %v, got %v", expected, json)
+	}
+}