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.
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.
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.
Use escape sequence for DELETE character.

This is just to make it a bit clearer what's going on.
Merge pull request #1217 from jacob-carlborg/isemail_unittests

Enable a bunch of tests for std.net.isemail.
Merge pull request #1176 from jmdavis/deprecated

Remove some undocumented, deprecated functions which are slated for removal.
Fix typo in comment
Merge pull request #1181 from monarchdodra/convEscape

Bugfix in std.conv.parseEscape
Add `std.traits.isNestedFunction`.

As I see no cases where nestidness check for both types and functions is required a new `isNestedFunction` template is created instead if adding an overload to `isNested`.
Merge pull request #1220 from denis-sh/add-trait-fron-nested-function-check

Add `std.traits.isNestedFunction`.