Bugfix in std.conv.parseEscape

parseEscape was not parsing the escapes:
\
0
'
"
?
unittests for parseEscape
Update unittest to take into account...

...Octal escapes and named character entities. These still don't work, but there was a test checking octal would throw, which is wrong.
Fix strideBack for ref ranges.
Added tests for reference type ranges to stride.
Fix for issue# 9456.

This change makes it so that decodeFront takes its range by ref and pops
off the code units that it decodes (unlike decode). It pretty much has
to do that, since it supports input ranges, and they can't do anything
else.
Swap a couple of overloads in std.utf.

This makes no semantic difference to the code, but it makes it so that
the attributes which are on one of the overloads don't make it into the
documentation (where they would imply that all of the overloads have
those attributes, which is not correct).
Minor tweak to decodeFront per review.
Add `std.traits.{isNested,hasNested}`.
Fix `std.traits.FieldTypeTuple` for structs.
Document what exactly `std.traits.FieldTypeTuple` do.
Remove some undocumented, deprecated functions which are slated for removal.

These have been deprecated for a while, but there was some balking
(primarily from Andrei IIRC) at actually removing them when they were
slated for removal, so they were instead made undocumented and slated
for removal after yet another 6 months or so. So, now that that time has
passed, here's another attempt to actually remove them.
Fix issue 4909
[whitespace] Fix spaces in `std.math.FloatingPointControl` example and unittest.
Fix `std.math.FloatingPointControl` two issues.

1. Do not call `setControlState` in destructor if not initialized (previously results in enabling all exceptions).
2. Call `initialize` on setting rounding mode (previously not called).
[docs] Improve `std.math.FloatingPointControl` example.
std.array: Fix inefficient appending of const(char)[] (Issue 9725)
Merge pull request #1209 from CyberShadow/fix9725

std.array: Fix inefficient appending of const(char)[] (Issue 9725)
Fixes Issue 9753 - Remove unnecessary asserts.
Merge pull request #1211 from AndrejMitrovic/Fix9753

Issue 9753 - Remove unnecessary asserts.