strings - Expand concept by newline and text blocks

[fapdash]

pull request

• Add multi-line strings / text blocks (Java 15)
• Add explanation of newlines / end of line chars, so students can understand the motivation behind text blocks

---

Noticed that the String concept was lacking text blocks.
While there are quite some details and intricacies to text blocks, they're not relevant for the level of detail the syllabus is aiming for, therefore it doesn't make sense to have them as an extra concept imo.
I added infos about newlines so students can appreciate the motivation behind text blocks.

Looking forward to your feedback. :)

---

Reviewer Resources:

Track Policies

[fapdash]

Not sure if system dependent newlines are too much information for this concept?

I've looked at how other tracks are testing multi-line strings. Elixir uses highschool sweetheart, which asks you to print a multi-line ascii heart. but I'd rather not swap out the whole exercise.

Maybe tell the students that the system should be able to produce a "fancy" message with the log level?

logLevelMessage("warning");
=>
┌───
│   Exercism Log System
│   Level: warning
└───