add support to ip range and limit remote to ip address only

proxifier would pass ip address to proxy with "Resolve hostnames through
proxy" turned off
add support for CIDR
ignore "cow" instead of "cow-proxy"
build script: use gnu-sed and build for darwin amd64 only
remove builtin sites (which are domains)
optimize hostIsIp
decrease number of limit on retry
remove PAC server
make http proxy only available for connection to port 80