🔃 Add ElementAtIndex function

his commit adds several new features and examples to the C# kernel syntax project, which demonstrates how to use the WriterSkill functions and the planning framework in C#. The main changes are:

- A new skill, MiscSkill, that provides some utility functions for working with lists and strings. This skill is used in the book sample to extract the chapter synopses from the novel outline.
- A new example of creating and executing a book creation plan, which uses the WriterSkill functions and the planning.BucketOutputs function to generate a novel with chapters, themes, and synopses.
- A new chapter for the Thinking Caps story, a mystery novel that is generated by the book creation plan. The new chapter introduces the main plot of the case of the missing mascot, and shows the characters' skills, personalities, and teamwork.
- A new skill for getting an element from an array at a specified index. This skill has a config.json file and a skprompt.txt file that define the input parameters and the prompt for the skill. The skill returns the element or an error message.
- Some minor fixes and improvements to the existing examples, such as fixing a typo in the email plan example, and removing the redundant output of the previous examples.