This commit converts primitive_types4 to a test and asserts that the
slice given is equal to the expected slice.
The intent of the primitive_types4 exercise appears to be to ensure the
user understands inclusive and exclusive bounds as well as slice syntax.
`rustlings` commands using `compile` do not verify that a specific
println is reached and, in the case of `watch` and `verify` (but not
`run`), they do not output the `println`s at all.
This fix is semantically similar to #198. It does not take a stance on
the correct way to handle this for all exercises; see #127. There are
likely other exercises whose intent are masked by this issue.
Sub READMEs contain the relevant resources from the main
README of the web version. All second edition Rust Book links
were updated to the 2018 edition.
Fixed to typos in main README.md.
