[MJAVADOC-722] Allow Logging Javadoc Warnings and Errors to File

**[Alan Zimmer](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=alzimmer)** opened **[MJAVADOC-722](https://issues.apache.org/jira/browse/MJAVADOC-722?redirect=false)** and commented

Allow for Javadoc generation, either implicitly or through a new configuration, to generate a file containing the warnings and errors that were found during Javadoc generation. Possibly following a similar pattern to the argfile  and options that are generated containing parameters passed to Javadoc create an errors files that will be placed in the Javadoc output folder that is ignored during Javadoc JAR creation.

This change would allow for CI systems to run Javadoc builds in parallel while still easily capturing any errors without the need for complex logging systems and would strongly ensure that there is a unique error report for each project.

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**Remote Links:**
- [GitHub Pull Request #159
](https://github.com/apache/maven-javadoc-plugin/pull/159)

Review pull request #159 and the Maven Javadoc plugin's existing argfile and options-file generation described in the issue. Determine how Javadoc warnings and errors are captured and where generated files are placed, then verify that the resulting report is unique per project and excluded from Javadoc JAR creation.

Written by the indexing model from the issue text.