Merge with default (code freeze for 1.0)
csv: always write summary info if file handle is open

fixes behavior of --csv FILE --log full
rest: initial documentation for threading details and considerations
fix WP issue for 422 and 444 format
slicetype: pre-calculate cost estimates for B slices, simplify callback

rate control was always calling back for B slice estimates but since we were
only pre-calculating them if VBV was enabled we were forced to make the
estimates at that time (withing the context of the API thread).

With this patch, we estimate B costs unless CQP is in use, and this allows us
to simplify getEstimatedPictureCost()
Merge with stable