Added fill() to manual/arrays

This is a combination of 3 commits
added fill() to manual/arrays
Backport of f466dfcc2bcde51755c9b7a9d58a484b55de8e48

added definite articles to fill! docs
Backport of b4e742cfed1884bab034e032e97ac17890f5c6f5

one more 'the' for fill
Backport of 6e685c31156b30632a7e40d9cb5f699f79c7546f