regexp_scan()
  Primitive regexp pattern scanner.
  
  There can be more patterns for one virus. All patterns in []
  must match to assign an buffer as virus (AND opeator).
  There can also be more virnames in one dictionary.
  
  Usage: regexp_scan([['VirName', 'RegExp_Pattern...'], ...], size=0, flags=0)
  
  Where: 'VirName' is a string, which identifies defined virus
         'RegExp_Pattern...' is a regexp pattern
         size is a number, which defines, how many bytes may be checked.
           If it is 0 or not defined, whole buffer is scanned.
           If it is -1, email header is scanned.
         flags is an integer, which defines regular expression flags.
           By default no flags are used.
    
  Example: regexp_scan([
             # Scan for a part of EICAR virus test file pattern
             ['EICAR', '^X5O!P%@AP[4.*EICAR-STANDARD-ANTIVIRUS-TEST-FILE'],
             # Scan for a an EXE file pattern endoded as base64.
             ['UnknownEXE', '^TVqQ']
           ])