HTTP Compression support

Added HTTP Compression support as requested in #10.

To enable compression support on HttpServer

```ruby
server.compression = true
```

to check support 
```ruby
server.compression  # returns the actual compression support value
server.compression? # alias for the above method, better for conditions
```
In HttpClient you can enable compression as follows
```ruby
client.compression = true
```
to check compression 
```ruby
client.compression  # returns the actual compression support value
client.compression? # alias for the above method, better for conditions
```

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