Use assert(false) instead of FIXMEs to quickly pinpoint missing features
Add support for extended characters not in CFR-2007-title47-vol1-sec15-119.pdf

http://en.wikipedia.org/wiki/EIA-608#Characters
http://www.theneitherworld.com/mcpoodle/SCC_TOOLS/DOCS/CC_CHARS.HTML
Let extended characters replace the previous character

This seems to be assumed by captions_cpc.scc and spanish.scc