Merge: doc: fixed some typos and other misc. corrections

This PR is fairly basic and only contains the following changes:
- Corrected various sentence structures, typos and text formatting across several markdown pages (language doc, README, etc.)

Note: There are a few sections I would rewrite differently to sound more professional/neutral and to include more details about how the language behaves in certain cases, but I felt like it was outside of this PR's scope.

Pull-Request: #2833
Reviewed-by: Jean Privat <jean@pryen.org>