#157 Improve Py3 MAPI string handling

[Nick Czeczulin]

Any mapi module functions that use the TCHAR typemap create some interesting challenges.
In Py2, passing a unicode string require it to first be encoded as utf-16le as well as setting the MAPI_UNICODE flag. In Py3, you can only pass unicode strings (and also must still set MAPI_UNICODE).
While in Py2 this is a reasonable workaround, for Py3, some mapi functions simply will not work with unicode strings and will always fail with MAPI_E_BAD_CHARWIDTH.

Note, this patch has a dependency on [#156] for its PyWinObject_FromMAPIStr() function.

It also introduces a new helper function PyWinObject_AsMAPIStr() which should keep things backward compatible with the existing workaround for Py2 mentioned above.

The bulk of this patch is adding implementations for anything that uses a TCHAR typemap. Anything that is currently documented as a deprecated MAPI method was not changed. This includes everything in the exchange sdk module, as well as a few methods in the mapi module which were annotated with a Deprecated MAPI function comment.

[Mark Hammond]

This looks like an improvement, thanks!

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