Add documented unit tests for formatValue()

Add example showing how to forward format specifiers.
Add example highlighting the similarity with formattedWrite(), and
comparing their use.

Change /** */ for /// and add $(D formatValue)

Replace /** */ with /++ +/
Issue 13013 - Converted real to double in std.json.JSONValue
std.algorithm.remove: Fix constraints and change popBack loop to popBackN
std.algorithm.remove: Change pop____N to pop____Exactly
Merge pull request #2291 from markisaa/realToDouble

Issue 13013 - Converted real to double in std.json.JSONValue
Updated std.format documentation of width and precision specifiers
Merge pull request #2302 from dcarp/master

Updated std.format documentation of width and precision specifiers
fix Issue 10916 - toHash on VariantN not being recognised

Make VariantN.toHash() const nothrow @safe. Assume that `VariantN.type` property is @safe nothrow.
Remove redundant Tuple.opEquals

Today struct type equality `a == b` is expanded to `a.tupleof == b.tupleof`, so opEquals method is unnecessary for `std.tyoecons.Tuple`.
Merge pull request #2303 from 9rnsr/fix_hash

Tweak Tuple and Variant for correct hashing
Merge pull request #2256 from Safety0ff/popbackn

std.algorithm.remove: Fix constraints and change popBack loop to popBackN
Fix issue 12455 [reg]Bad lowercase mapping for 'LATIN CAPITAL LETTER I WITH DOT ABOVE'

Also as part of a fix restores a test case in string.d
to exactly match older behaviour.

Some extended greek is not upper but title case, yet changes on toUpper.
Merge pull request #2296 from Element-126/doc_formatValue_add_example

Add documentation examples for formatValue()
std.json.JSONValue toString is now const
Merge pull request #2292 from markisaa/constToString

Issue 13015 - std.json.JSONValue's toString is now const
Merge pull request #2304 from DmitryOlshansky/issue-12455

[REG]Fix issue 12455 Bad lowercase mapping for 'LATIN CAPITAL LETTER I W...