convert_hex 0.2.0

Hexadecimal conversion for easier adjustment

[0.2.0] - Support null safety.

• Edit class Hex to ConvertHex
• use function convertHex

[0.1.7] - Fix Base 16

• Fix function Hex charDecode and charEncode

[0.1.6] - Fix Base 64

• Edit how to use hex64
• Add return StatusEncode in encode Hex64

[0.1.5] - Add Base

• Add Convert Hex64

[0.1.0] - Base Hex

• Convert Hex