add a second context.
do a System.exit to terminate all threads.
add parsing to Scheme itself.
add X-Forwarded-* headers.
add Host header.
Rename setOption to set and add methods to add/set multiple header values.
refactor Headers accessors to have less duplicated code.
Refactor out AcceptValue(s) and change Accept-Encoding header to the new design.
Add more accept headers.