# convert text file into c string
sed -e 's/\\/\\\\/g;s/"/\\"/g;s/\t/\\t/g;s/^/"/;s/$/\\n"/' <file>

# something else... with explanation
sed -n '/## Screensh/,/##/{/Scree/{p;n};/##/{q};p}' file

-n                 -> not print
'/## Screen/, /##/ -> match range, I guess you knew it already
{                  -> if in this range
    /Scree/        -> and line matches /Screenshot/
        {p;n};     -> do print line, and read next row (skip doing rest processing)
    /##/           -> if line matches "##"
        q;         -> quit, we have done all printing
    p              -> if we come to here, print the line
}