bug fix

• fix #250 case insensitive field match
• explit test case sensitive for #252
• fix #261 should load from reader
• fix #260, support rename for extra.SupportPrivateFields
• fix #263, support empty string as 0 in fuzz mode
• fix #264 check io.EOF when test decoder.More
• fix #274, unescape before base64 decode
• Merge pull request #282 from caesarxuchao/optional-case-sensitivity
• fix #276 allow rename when set naming strategy