refactoring, add PDF prefix
add static library target
add PDFEncodingDifferences
rewrite parsing in PDFCMap
readding PDFEncodingDifference
fix PDFFontDescriptor issue with possible lack of a type key
fix an issue with an unknown unicode symbol in PDFFont
add support of Encoding Differences to SimpleFont
fix an issue with an unknown unicode symbol in Type0Font
add widthOfSpace method to PDFRenderingState
improve handling of newline and whitespaces in PDFScanner
use SimpleFont.encodingDifferences and RenderingState.widthOfSpace in PDFScanner.didScanCharacter method