Move clean-up code to its own method

Clean-up consists of purging the temporary folder.
At the high-level, details of this implementation are not needed.
It is clearer to have a dedicated method for this.
Also, we might want to use it in other places (eg in Exception handling).
Fix styling/PEP8 issues
Remove unused imports
Replace deprecated module with built-in method

Replacing in string is built-in, no need to use the
indeed deprecated string.replace
Specify Exception type

In this try block, with the statement `import pyPdf`,
we are expecting a possible ImportError exception.
Explicitly catching this type.
Remove unused argument from main method

The 'verbose' argument is unused - a left over from a different design.
Removing it.
Use join instead of os.path.join

Fully importing os.path.join, to add clarity
Split long string lines

Using Python built-in string concatenation to avoid
a giant unreadable line.
Remane some variables to avoid reserved words