if thumbnail error thrown, handle as warning not Error
control path of ffmpeg execution for some processes
add option to use 'cat' instead of ffmpeg concat
a number of improvments for more stability

- remove default built in logging callback
- ensure times are localized to US for command line
- ensure canonical paths are used
ensure Locale.US timezone and canonical paths
more fixes for time management
fixes for audio sync
Merge pull request #12 from n8fr8/master

more tweaks for StoryMaker