Handbook for 3.4

To-dos:

Replace versions "3.3" with "3.4"
Check the changelog to see if it affects the handbook
Go through handbook and see if anything seems worth to be changed
Add section about the python scripts in bin directory #1019 (closed) !2587 (merged)
Change package name scrpage2 to newer version scrlayer-scrpage (!2556 (merged))

Edited May 05, 2021 by Farid Mohammadi