Implement coffee machine program and tests (MIL-002)

Add the Menu, MenuItem, CoffeeMaker and MoneyMachine classes with the
assignment's method names, and a main loop that supports drink names,
report and off. Resources are checked before payment, and payment
before the drink is made.

Move drink prices, ingredient amounts and all message text into
constants.py. Add 25 pytest tests for every class and the main loop,
and record the review against QC-PY-001 as RC-007.

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6
Closes #6
Closes #7
Closes #8
Closes #9
Closes #10
Closes #11

src/coffee_machine/__main__.py

@@ -0,0 +1,7 @@
+"""! @file
+@brief Allows `python -m coffee_machine`.
+"""
+
+from coffee_machine.main import main
+
+main()