fresh

HTTP response freshness testing，it is copied from fresh by golang.

• RequestHeader
• ResponseHeader

req := httptest.NewRequest("GET", "/users/me", nil)
resp := httptest.NewRecorder()
// true
Fresh(req.Header, resp.Header)

• modifiedSince IfNoneMatch of request header field

• noneMatch IfNoneMatch of request header field

• cacheControl Cache-Control of request header field

• lastModified LastModified of response header field

• eTag ETag of response header field

Check([]byte("Sat, 01 Jan 2000 00:00:00 GMT"), []byte("\"foo\""), nil, []byte("Sat, 01 Jan 2000 00:00:00 GMT"), []byte("\"foo\""))