Bug Fix: Multiple notes with same name used to overwrite each other.

Builds a unique file name for each note to avoid conflicts by appending a suffix. 

Example: You have three notes, Semester 1/Timetable, Semester 2/Timetable and Semester 3/Timetable. 
Old behaviour: Each one of these would overwrite the previous when it was outputted since notebooks are not exported by Evernote to the *.enex file. Output is therefore the last note to be processed as Timetable.md. 
New behaviour: A suffix is added to each so the names don't conflict. All notes are outputted as Timetable.md, Timetable (1).md and Timetable (2).md.