Merge branch 'ackermann'

The series.py and ackermann.py work is done.
Merge remote-tracking branch 'upstream/master'

Incorporating any changes from upstream master to my local
repository.
Add list_lab.py
Ack and Series Python files added
Merge remote-tracking branch 'upstream/master'
Add fruit_list and print it
Add input request and expand the fruit_list
Complete first draft of series 1 list creation
Modifications to Ack and Series files.
List_lab.py added to student directory
Merge remote-tracking branch 'upstream/master'
Add _validate_input() to list_lab.py to check user input against expected values
List_lab.py added as final version.
Add _print_list() to print each element of a list for asthetics
Replace _print_list() with _print_basket() to reduce print statements
Add first draft of series 2
Add print messages indicating changes to the fruit list that are outside user control
Add draft of series 3 and 4
Fix print formatting
Make _validate_input() case insensitive