Added implementation in common lisp with unit-test

- added the existing implementation in common lisp with system-definition
- added a parachute-unit-test
- added a description for setup and running the unit-tests
- added a description for stubbing and mocking with cl-mock

common-lisp-parachute/README.md

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+# gilded-rose
+
+## Setup
+
+### Install quicklisp
+
+To run this project install quicklisp (if not already done): 
+ - download https://beta.quicklisp.org/quicklisp.lisp
+ - load it with your common lisp implementation. The example with sbcl: 
+   > sbcl --load quicklisp.lisp
+ - run the command 
+   > (quicklisp-quickstart:install) 
+   in your common lisp implementation
+ - run the command 
+   > (ql:add-to-init-file) 
+   in your common lisp implementation
+
+### Install project
+Copy the project-folder containing this file into /quicklisp/local-projects/ that has been created when installing quicklisp.
+This is the root directory for quicklisp to search for the gilded-rose.asd file which defines the system (project) and its dependencies.
+The quicklisp-folder is usually created in your home-directory.
+
+### Work with the project
+
+Now you can load the project with 
+> (ql:quickload "gilded-rose") 
+in your common lisp-implementation and run the tests with 
+> (asdf:test-system "gilded-rose")
+.
+
+You can stub and mock functions and methods with the cl-mock-library which is already included in the system definition of the test-system:
+
+(with-mocks ()
+  (answer <your-method> (call-previous))
+  (<your-method> <argument-list>)
+  (is <your-testcase> (invocations '<your-method>)))
+
+## Documentation
+
+Hi and welcome to team Gilded Rose. As you know, we are a small inn
+with a prime location in a prominent city ran by a friendly
+innkeeper named Allison. We also buy and sell only the finest goods.
+Unfortunately, our goods are constantly degrading in quality as they
+approach their sell by date. We have a system in place that updates
+our inventory for us. It was developed by a no-nonsense type named
+Leeroy, who has moved on to new adventures. Your task is to add the
+new feature to our system so that we can begin selling a new
+category of items.
+
+First an introduction to our system:
+ - All items have a SellIn value which denotes the number of days we have to sell the item
+ - All items have a Quality value which denotes how valuable the item is
+ - At the end of each day our system lowers both values for every item
+ 
+Pretty simple, right? Well this is where it gets interesting:
+ - Once the sell by date has passed, Quality degrades twice as fast
+The Quality of an item is never negative
+ - "Aged Brie" actually increases in Quality the older it gets
+ - The Quality of an item is never more than 50
+ - "Sulfuras", being a legendary item, never has to be sold or decreases in Quality
+ - "Backstage passes", like aged brie, increases in Quality as it's
+   SellIn value approaches; Quality increases by 2 when there are 10
+   days or less and by 3 when there are 5 days or less but Quality
+   drops to 0 after the concert
+
+We have recently signed a supplier of conjured items. This requires an update to our system:
+ - "Conjured" items degrade in Quality twice as fast as normal items
+
+Feel free to make any changes to the UpdateQuality method and add
+any new code as long as everything still works correctly. However,
+do not alter the Item class or Items property as those belong to the
+goblin in the corner who will insta-rage and one-shot you as he
+doesn't believe in shared code ownership (you can make the
+UpdateQuality method and Items property static if you like, we'll
+cover for you).
+Just for clarification, an item can never have its Quality increase
+above 50, however "Sulfuras" is a legendary item and as such its
+Quality is 80 and it never alters.
+