[x265] Preset superfast undocumented in help output and PDF page 3

[Mario Rohkrämer]

There is a preset "superfast" which is missing in the help output of x265  
and in the verbose explanation of command line options in the Evaulator's  
Guide on page 3. But it appears in the table of quality presets on page 9  
and is available while encoding.

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Fun and success!
Mario *LigH* Rohkrämer
mailto:contact at ligh.de