avro

Allow to set template dir for avro-tools compile

maven-avro-plugin allows to specify custom template
directory (https://issues.apache.org/jira/browse/AVRO-983), same
applies to
gradle-avro-plugin (https://github.com/commercehub-oss/gradle-avro-plugin#templatedirectory).

It would be useful to support that in Arvo CLI tools as well. Use
case: generating Java classes during CI or for any scripting needs
when using maven or gradle plugins is too much