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.
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.
Remove unnecessary cast

That has changed in https://github.com/D-Programming-Language/druntime/pull/359
Merge pull request #1212 from 9rnsr/fix_ti_next

Remove unnecessary cast
Improve scoped
Merge pull request #1215 from monarchdodra/scope

Improve scoped implementation
Enable a bunch of tests for std.net.isemail.

These tests were previously commented out because of a bug
the regular expression module. Now when we have a new regular
expression module we can enable these tests.

This also fixed a bug in the internally used "substr" function.