Add new voice character for SANTA and BEAR

Dear pchw-san

Thank you for using this useful library.

According to below API doc, SANDA and BEAR character is added.
[https://cloud.voicetext.jp/webapi/docs/api](https://cloud.voicetext.jp/webapi/docs/api)

I'd like to support these character. Then I have sent this pull request.

Thank you very much in advance for your kind cooperation.