#4 Fixes for C API

[toiffel]

Hi,

The attached patch resolves some issues with Bento4 C interface:

• Fixed declaration of AP4_SyntheticSampleTable_AddSample
• Fixed a couple of typos in Bento4C.h
• Added missing interfaces for AP4_FileCopier and AP4_FileWriter

Please review it and apply to SVN trunk. Thanks.