SimpleDB: add a solution or link to with more match

[amanjeev]

https://github.com/ferrous-systems/rust-exercises/blob/main/exercise-book/src/simple-db.md

Add more match. more match more match! chant grows!

cc @miguelraz

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[miguelraz]

I think it would be nice to sequence this exercise in a way that helps people leverage the pattern matching powers of match, not just showing the solution at the end.

Also, there can be a trailing data corner case by not checking that the first newline is the end of the data.

Leave it as an extra credit, along with a "try to do it with a single match"?

[jonathanpallant]

I had an idea to simplify this example - don't require the terminating newline, and change the spec to say that all leading and trailing whitespace is trimmed before processing.

[jonathanpallant]

Running through this again, I think the first-pass solution should probably be:

1. Does this string have exactly one newline in it?

   input.chars().filter(|c| *c == '\n').count() == 1

2. Does this string have a newline at the end?

   input.chars().last() == Some('\n')

This builds on the iterator lesson, without needing to know weird string functions.