Fix concetion pool & timeout (issues #82)

[zamanimehdi]

ref: #82

[ganmacs]

Commits about #80 are included.

[repeatedly]

pool and timeout default values are same with ActiveRecord?

[zamanimehdi]

pool and timeout default values are same with ActiveRecord?

In non-parallel applications, requests sent via activerecord do not require a large amount of parallel request and connection pool, while in fluentd parallel transmissions , the amount of connection pool must be able to cover the number of simultaneous requests.
Therefore, activerecord connection pools must be greater than parallel fluentd threads.
On the other hand, according to bulk-insert, the value of timeout should be more than the usual requests.
The default values are set based on my own experience of working with fluentd.

[repeatedly]

Thanks. This patch will be included since v2.0.0.