Add JavaDocs to classes, fields and methods, as well as the return and parameter arguments for each method

[MrCrazys]

• Every class, field and method has a JavaDoc now.
• Certain methods have nullability annotations now.
• Fixed grammatical errors.
• Deprecated method newList(Object...) as the name was misleading (it isn't clear that it creates a new ArrayList; you would have to look at the source code to see that). I have renamed it to newArrayList(Object...). This makes it more consistent with the newHashMap(Object, Object) method, which has a good name that makes it obvious what type of Map is being created.
• Deprecated method newSet(Object...) as the name was misleading (it isn't clear that it creates a new HashSet; you would have to look at the source code to see that). I have renamed it to newHashSet(Object...). This makes it more consistent with the newHashMap(Object, Object) method, which has a good name that makes it obvious what type of Map is being created.
• Removed calls to the newList(Object...) method and replaced it with the newArrayList(Object...) method.
• Changed the semantics for certain parts of the code (for example, replacing Map.entrySet().forEach() with Map.forEach()).
• Removed redundant escapes for regular expressions.

[kangarko]

Thanks, I'll pull it manually later.

We can't rename methods because it will break all programs our students are using for now, I only do this on major version bumps (i.e. 5.0 to 6.0) so I can't pull this commit entirely.

[MrCrazys]

Alright, that's okay. Just a personal preference I suppose. It doesn't really matter. Just happy to contribute!