Ascii85 aka Base85 更高效的binary->ascii编码

Ascii85 (also called "Base85") is a form of binary-to-text encoding developed by Paul E. Rutter for the btoa utility. By using five ASCII characters to represent four bytes of binary data (encoded size 25% larger), it is more efficient than uuencode or Base64, which use four characters to represent three bytes of data (33% increase).

Its main modern use is in Adobe's PostScript and Portable Document Format file formats.

能提高点效率是一点，反正编码也简单。