Support gzip by default

[mrjoelkemp]

Ref https://github.com/3rd-Eden/npmjs/issues/4#issuecomment-151009538

We could either allow consumers of mana to supply an override for a gzip option, or always support it.

I'm in favor of the latter, which would require a one-line addition to the definition of the send function.

Any interest in getting this patched?