FlatCC FlatBuffers in C for C Files

Release 0.6.3 is a point release immediately following 0.6.2 because the master branch would report flatcc --version as 0.6.2 instead of 0.6.2-pre prior to the 0.6.2 release and version comment in generated headers would do the same. By bumping to 0.6.3 ensures that 0.6.3 is indeeded a release version and not a development snapshot. 0.6.3 is unctionally equivalent to the 0.6.2 release.