History of Number.prototype.toLocaleString()

Safari 10 for both macOS and iOS supports the locale and options arguments

Add "Return value" section as per Bug 1287421

Fix anchor

Fix invalid char in code example

add more specs

clr review

Added note that feature detection using try..catch doesn't necessarily work in ECMA-262 Ed 3 hosts.

Add simpler, more efficient feature detection without resorting to try..catch.

Changed 'real Arabic' to the correct designation 'Western Arabic', and 'English digits' to 'Eastern Arabic digits'. Reference: https://en.wikipedia.org/wiki/Arabic_numerals