Merge pull request #23 from aerenchyma/add_review_prblms1

Add first review problems
small changes to Review exercises
PS4 draft added to assignments
revised Functions chapter, part I
made language for test_questionfunctions_2a and 2b more clear
got rid of str+int issue in ch04_square
removed exercise header (because there are no exercises)
made last two questions func-12 and 14 get compiled
fixed test_functions_2_4
removed test_questionfunctions_2_1 because it was not covered in the chapter
changed prints to not print out a tuple
Revert "removed test_questionfunctions_2_1 because it was not covered in the chapter"

This reverts commit 2aeec302e09ae1917a14f5ead17b0b9f87dfec79.
added explanation that return ends function execution
refactored assignments into separate files for each week
bug fix
small fixes to PS5
remove Functions/temp.rst
added assignment/student page which will house grades for all assignments
added grade link to index
added grade controller