Add JSON Helpers to TJsonObject for Delphi XE+

Addressing
https://github.com/fabriciocolombo/delphi-rest-client-api/issues/17
WinInet constants for Delphi XE compatability

The constants defined for Delphi < XE were introduced in XE2 so should
be defined for Delphi < XE2.
Revert "Add JSON Helpers to TJsonObject for Delphi XE+"

This reverts commit e9569c01fe35d034dae796a79b9bc3a230d403a1.
The property AsInt64 of TJsonNumber was included from Delphi XE2. Fixes #17 and closes #18
Remove backup *.~inc files from source directory

``DelphiRest.~inc`` doesn't need to be in the source. I've deleted it
and added a ``.gitignore`` entry to stop future ``.~inc`` files being
added.
Merge pull request #20 from thatalextaylor/master

Internet options for WinInet need to be defined for Delphi XE