`/more/` should include context for the matching lines

[cnst]

Since the /more/ page is already somewhat relaxed, providing more in-context results compared to the original search results from which it is linked from, it might as well include some context to the lines found — perhaps a standard 3-lines before, 3-lines after, would nice.

For example, in the nginx source, I want to figure out what diagnostic messages are available with each log level, for error_log. However, /more/trunk/src/http/ngx_http_request.c?refs=ngx_log_error page only lists the actual levels, but doesn't list the text message of the warnings, making the grokking difficult.

[tarzanek]

see #638 - I think the request for config lines is there, too
I won't close this as dup because this is for "more" page