Fix various small typos in code, Javadocs and documentations.

Some sentences has been slightly simplified (e.g. all of the -> all the, or whether or not -> whether). And some formatting has been added to improve readability (e.g. the accept header -> the {@code Accept} header).

Comment From: snicoll

@philwebb can you share what amendments are needed? Perhaps @marcwrobel could update their PR based on the feedback.

Comment From: philwebb

I'm not sure why I added merge-with-amendements, perhaps it was because I thought some changes would be required to apply the fixes to 2.6.x. Turns out it applied pretty cleanly.

Thanks for the PR @marcwrobel! Much appreciated.