Limit number and lifetime of connections (#208)
Limit number and lifetime of connections (#208)

* Limit number and lifetime of connections

https://golang.org/pkg/database/sql/#DB.SetMaxIdleConns
https://golang.org/pkg/database/sql/#DB.SetMaxOpenConns
https://github.com/golang/go/commit/0c516c16328575ab78a4cce49874955dd590efa2

* by design exporter should use maximum one connection at any given time

* Capitalize sentences and re-word them.

prometheus/mysqld_exporter,prometheus/mysqld_exporter,roman-vynar/mysqld_exporter,roman-vynar/mysqld_exporter