Combined features from few PRs into one + some other additions and dual-build

[saper-2]

• I had some issues with my Chinese portable recipe printer (with USB/BT interfaces), so I did some fixes - mainly the one that define in image rendering how much printhead have dots - this one now can be set in Printer property and will be passed to image rendering routine - before it was hard-coded to 576:
  

  ESC-POS-USB-NET/ESC-POS-USB-NET/Epson Commands/Image.cs

  Line 16 in ff50466

  double multiplier = 576; // this depends on your printer model.

Now it can be set like this (before calling prn.Image):

ESC_POS_USB_NET.Printer.Printer prn = new ESC_POS_USB_NET.Printer.Printer(eSelPrinter.Text);
prn.DotsInLine = Convert.ToInt32(ePrintingDots.Value);

• Also I have changed in project file TargetFramework so the build will be not only for netstandard2.0 but also for net45 - this should make easier to include only the library dll itself with netFramework application (net 4.5+)

• Another changes are in Code128 - now it's possible to specify charset A/B/C - like Barcode128 only allows C code charset #38 ,and I took it a step further and added to all barcodes a options that allow to set length(height) and width (module) .

• Added also Reverse mode like in PR Implemented reverse mode #47 .

• Next change is in Image routine again, I have added option scaleToWidth - this behave almost like PR Image print isScale and center #68 , but my twist it that if image is wider than printhead width then image will be down-scaled to printing width. As for center feature, I think adding AlignCenter before image should do the trick (unfortunately my chinese MPT-II don't support centered images).

• Another changes are in regards to QrCode - many of those changes are from PR add Qrcode size(normally 16 kind of size and default is 3+) #22 , I have added a function that allow to set size, error correction level, and option to disable Set QrCode Model command: GS(k<func165> , my printer instead ignoring this command it print a number 2 😒 - it took me a while to figure it out (I had for a while: wth this 2 is coming from 😠 )

• Lastly I have updated README , added CHANGELOG file and file SPECIFIC-PRINTER-INFO where we maybe put together some information about different printers and theirs quirks.