Cinema4D (.c4d) support for Assimp through Melange

Melange is Maxon(tm)'s proprietary interfacing library to read and write C4D files and it is a necessary dependency for assimp-cinema4d. For this reason, this code lives in a separate repository to make clear that it has proprietary dependencies and is therefore not fully free software (and its use is subject to the Melange terms of use).

To build:

• clone from https://github.com/acgessler/assimp-cinema4d
• download melange (v6) from www.plugincafe.com and put it into contrib/ so that contrib/Melange/_melange/includes and contrib/Melange/_melange/lib/WINare available.
• run cmake, enable the ASSIMP_BUILD_NONFREE_C4D_IMPORTER flag
• build either DEBUG or RELEASE with VC9, VC10 or VC11 (only these will work as these are targets supported by melange)

Currently no other targets other than Windows with MSVC are supported.