Changed copyright end year to 2020 in every reference "Copyright (c) 2006-XXXX, assimp team".
Changed copyright end year to 2020 in every reference "Copyright (c) 2006-XXXX, ASSIMP Development Team".
Changed copyright end year to 2020 in LICENCE.rtf.
Changed copyright end year in CMakeFiles.txt files and any other places referencing Assimp with a copyright start and end year.
Added the following functions:
* Flush() to flush the internal StreamWriter buffer to the stream
* Tell() gives the current stream position
* Seek() seeks to a given offset in the stream
* PutString(aiString&) to write an aiString
* PutString(std::string&) to write a std::string