Support more than 8192 byte data size

Hi, thanks for the great library. I found an issue while trying to read large amounts of data from the PLC. Data after ~8192 has quality "BAD undefined".

After some digging I found the buffer size is set to 8 kB:

nodeS7/nodeS7.js

Lines 2745 to 2752 in 44a1b5e

    
           // This is where the data can go that arrives in the packet, before calculating the value. 
        
           this.byteBuffer = Buffer.alloc(8192); 
        
           this.writeBuffer = Buffer.alloc(8192); 
        
           // We use the "quality buffer" to keep track of whether or not the requests were successful. 
        
           // Otherwise, it is too easy to lose track of arrays that may only be partially complete. 
        
           this.qualityBuffer = Buffer.alloc(8192); 
        
           this.writeQualityBuffer = Buffer.alloc(8192);

nodeS7/nodeS7.js

Line 1044 in 44a1b5e

dataBuffer = Buffer.alloc(8192);

Is there any reason to limit the size of buffers to 8 kB? I think most S7 PLCs support 64 kB DBs.

	// This is where the data can go that arrives in the packet, before calculating the value.
	this.byteBuffer = Buffer.alloc(8192);
	this.writeBuffer = Buffer.alloc(8192);

	// We use the "quality buffer" to keep track of whether or not the requests were successful.
	// Otherwise, it is too easy to lose track of arrays that may only be partially complete.
	this.qualityBuffer = Buffer.alloc(8192);
	this.writeQualityBuffer = Buffer.alloc(8192);