Fix double free and memory leaks

[mon]

Fixes #9.

ogg_sync_destroy frees ogg->state, which is then freed again by free(ogg). By allocating this separately and letting libogg free it this is avoided.

ogg_stream_init allocates 3 buffers, which are not properly freed. By separately allocating ogg->stream and calling ogg_stream_destroy, these are properly freed. Saves ~26kb of lost memory.

Finally, libogg recommends ogg_sync_pageout be called before ogg_sync_buffer to initialise some buffers. Added a call to it inside AVOggInit to follow this recommendation.

[Kukunin]

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