Added EXTERN_C to MRCP_PLUGIN_DECLARE macro, required for C++ plugins  issue-15
Added EXTERN_C to MRCP_PLUGIN_DECLARE macro, required for C++ plugins 
issue-15

AaronZhangL/unimrcp-1,unispeech/unimrcp,AaronZhangL/unimrcp-1,unispeech/unimrcp,unispeech/unimrcp,AaronZhangL/unimrcp-1