Adding "internal" middleware

- Detect too many internal redirects - return 500 in this case

- redirect internally regardless of proxy status code
- support multiple internal redirects

server: read -conf flag before reading stdin config 

tls: suggestion - disable tls if port is http?

core: Add the option to specify what address to bind on in Caddyfile

proxy: Refactor so that other upstream backends can be implemented

adding crypto/tls sessioncache

Refactor proxy middleware so that 1.) From() is exposed 2.) Other upstreams can be implemented/plugged in