Add replaces[].fromFlags for supporting flags of regular expression

[libook]

from is regular expression, fromFlags is flags of regular expression, and tois letter. In the internal from, fromFlags and to are used with String#replace(new RegExp (from, fromFlags), to).

  "plugins": [
    {
      "name": "./src/Plugin.js",
      "option": {
        "replaces": [
          {"from": "^src/", "fromFlags": "i", "to": "lib/"},
          {"from": "^lib/MyClass2.js", "to": "lib/foo"}
        ]
      }
    }
  ]