| Function silc_buffer_pull
 
 SYNOPSIS
 
    static inline
    unsigned char *silc_buffer_pull(SilcBuffer sb, SilcUInt32 len);
DESCRIPTION
    Pulls current data area towards end. The length of the currently
    valid data area is also decremented. Returns pointer to the data
    area before pulling. Returns NULL on error.
EXAMPLE
    ---------------------------------
    | head  | data       | tail     |
    ---------------------------------
            ^
            Pulls the start of the data area.
    ---------------------------------
    | head     | data    | tail     |
    ---------------------------------
            ^
    silc_buffer_pull(sb, 20);
 
 
 
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