Docs Update: Tutorials

[AadityaRajPaudel]

Addition of extra content for 'cons' function, and addition of definition of 'getf' function in Plists.

[AadityaRajPaudel]

Due to relative changes in the positions of texts after addition of extra contents in the tutorial.md file, changes are shown in many lines of code, but there are only 2 major points at which the changes are made, as mentioned in the two commits.

[daninus14]

Regarding the second commit: the formatting changes make it really hard to follow. I'm not opposed to the formatting changes, but it would make it much easier to understand if you had those in a separate commit. Can you undo that commit and split it into two?

Regarding the first commit: 3c4462d Unclear why you are using a defun over there, and it doesn't look correct either. Perhaps using an english sentence would be easier? You are also providing an implementation, which is basically incorrect to do so because that's up to the implementation to decide how to do it, not the language specification. I would actually be surprised if most implementations use recursion as you are.