FFmpegContext can now also hold a cursor over a vector of bytes instead of a cfile to store sound data in it.
Appropriate creation, reading seeking functions included.
This adds a mechanism for running generic operations at specific points
of the frame execution. This can be used by any part of the code an not
just Lua since it simply executes std::functions. It also adds an
"execution context" concept that specifies in which situation an
operation should be executed.
This is then used by the Lua Coroutines code for resuming coroutines at
specific points instead of always when the awaited promise resolves.
Invalid values previously corrupted the internal position counter which
caused crashes on some platforms because the position counter would
overflow in the next read operation. I added some assertions to track
the position counter corruption and it's probably a good idea to leave
them in to catch possible future errors early.
The actual fix was to just ensure that the seek position it always valid
for the file.
This fixes#1059.
the-maddin