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.
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