added have_cake_and_eat_cake_too (#906)

* added have_cake_and_eat_cake_too

* renamed effect_neg to effect_rem

* added have_cake_and_eat_cake_too to readme

* added details to Problems in planning.ipynb

Added more information for the problems Air Cargo, Spare Tire, Three Block Tower, Have Cake and Eat Cake Too.

* removed a test from planning.py

A test for three block tower problem is written here. I have removed it.

* Style fixes

* minor style fix

* fixed a typo

* minor fixes

some sentence issues

* minor changes

* minor fixes

Author: nvinayvarma189

README.md

@@ -111,7 +111,7 @@ Here is a table of algorithms, the figure, name of the algorithm in the book and
 | 10.1   | Air-Cargo-problem                 | `air_cargo`                   | [`planning.py`][planning]       | Done | Included |
 | 10.2   | Spare-Tire-Problem                | `spare_tire`                  | [`planning.py`][planning]       | Done | Included |
 | 10.3   | Three-Block-Tower                 | `three_block_tower`           | [`planning.py`][planning]       | Done | Included |
-| 10.7   | Cake-Problem                      | `have_cake_and_eat_cake_too`  | [`planning.py`][planning]       | Done |          |
+| 10.7   | Cake-Problem                      | `have_cake_and_eat_cake_too`  | [`planning.py`][planning]       | Done |     Included |
 | 10.9   | Graphplan                         | `GraphPlan`                   | [`planning.py`][planning]       |      |          |
 | 10.13  | Partial-Order-Planner             |                               |                                 |      |          |
 | 11.1   | Job-Shop-Problem-With-Resources   | `job_shop_problem`            | [`planning.py`][planning]       | Done |          |