Renamed project from 'PyPDF2' to simply 'PDF'

--HG--
rename : PyPDF2/__init__.py => PDF/__init__.py
rename : PyPDF2/_version.py => PDF/_version.py
rename : PyPDF2/filters.py => PDF/filters.py
rename : PyPDF2/generic.py => PDF/generic.py
rename : PyPDF2/merger.py => PDF/merger.py
rename : PyPDF2/pdf.py => PDF/pdf.py
rename : PyPDF2/utils.py => PDF/utils.py
rename : PyPDF2/xmp.py => PDF/xmp.py