Changes fall into these categories:
1. Avoid pathological string building. Loops over x = x .. "foo" can
become very slow. Instead, use strbuf.lua, table.concat, or just one
continuous concatenation; a = x .. y .. z is one operation, better than
a = x .. y; a = a .. z
2. Use hex-escaped strings instead of string.char. I find this more
readable in many cases, and it avoids a table lookup and function call.
3. Don't duplicate code. A few libraries and scripts had re-implemented
stdnse.generate_random_string or openssl.rand_bytes.
1. The first paragraph of a function's NSEdoc is used as a short
summary. Some of these were very long, so I split off a shorter summary.
2. Use asterisks (*) to denote bulletted lists, not 'o'
3. Wrap lines at 80 columns
4. a couple other spelling and formatting fixes
