Support v0.14, TCP+TLS protocol and config placeholder

[joker1007]

I forked remote_syslog_logger to support TCP+TLS protocol (https://github.com/reproio/remote_syslog_logger, released new version as remote_syslog_sender), And I re-implemented this plugin for fluentd-0.14.x.

This patch fixes almost issues.

• https://github.com/dlackty/fluent-plugin-remote_syslog/issues/10 (by remote_syslog_sender and new options)
• https://github.com/dlackty/fluent-plugin-remote_syslog/issues/13 (by refactoring logger creation timing)
• https://github.com/dlackty/fluent-plugin-remote_syslog/issues/18 (by fluentd-0.14.x feature)

I want to feedback upstream and to release new version. If you don't have enough time for maintainance, I can take over this plugin maintenance. I would appreciate it if you think about my proposal.