#2 add extern "C" to client library headers

[Jared Moore]

Hi,

It would be nice if extern "C" declarations were added to the headers of the C client library, just to make life a tiny bit easier for C++ programmers.

See [1] in case you don't know what I mean.

Cheers and thanks for the great work!

[1] http://tldp.org/HOWTO/Program-Library-HOWTO/miscellaneous.html#CPP-VS-C