Improve PDFDebugger of PDFBOX [PDFBOX-2530]

by Khyrul Bashar for Apache Software Foundation

PDFDebugger is a tool from PDFBox that helps the user to inspect the structure of a pdf file. Present PDFDebugger provides some useful features but also lacks some features those are necessary in PDF file debugging, e.g. a hex viewer. This project aims to add these functionalities to PDFDebugger with some other features that may make PDFDebugger more likable to users e.g. styled content stream for bracketing operators.