NEW ngx_http_geoip_module netspeed database support

This adds support for the Maxmind Netspeed database which maps the IP address a particular network speed. All changes are confined to the module ngx_http_geoip.

Documentation:
```
syntax: 	geoip_netspeed file;
default: 	—
context: 	http

Specifies a database used to determine the netspeed depending on the client IP address. The following variable is available when using this database:

$geoip_netspeed
    needspeed of the user, for example "Cellular" or "Cable/DSL"
```