Create GZIP writer for every compress request
Create GZIP writer for every compress request

The GZIP writer was being shared -- incorrectly -- by multiple HTTP
requests (both queries and executes). But it's not thread safe. Bad,
bad, bad.

https://github.com/rqlite/rqlite/issues/781

rqlite/rqlite,rqlite/rqlite,rqlite/rqlite