Escape all strings

[ups91]

This patch allow us escape not only valid json string, but any (selected) text.

[ghost]

Would you mind giving examples? Wouldn't it be better to make sure it's a valid JSON? It's a JSON tool after all :)

[taichunmin]

In my opinion, the isValid function should be change to:

public isValid(text: string): boolean {
  try {
    JSON.parse(text);
    return true;
  } catch (err) {
    return false;
  }
}

Because JSON can also be number, string, boolean or null.

• JSON website

[taichunmin]

For example, some programing language (like PHP) or IE will escape non-utf8 charset by default:

<?php
$a = "測試";
echo json_encode($a);

// "\u6e2c\u8a66"

If we can change the isValid function, then this string is also be supported.