Support writing Javadocs in Markdown style (JEP 467)

[pbi-qfs]

Closes #234

Before this PR

It was not possible to specify JEP 467 style for markdown Javadoc.

After this PR

With the additional CodeWriter flag it is possible to output Javadoc in JEP 467 style:

package com.example.empty;

import java.lang.Void;

/// # Empty Class
///
/// A representation of nothing: /* empty */
///
/// This is not to be confused with the [Void] datatype which
/// is an uninstantiable placeholder class to hold a reference
/// to the *Class* object representing the Java keyword `void`.
class EmptyClass {
}

Possible downsides?

To use the alternative Javadoc style, a flag must be specified for the JavaFile builder or
a dedicated CodeWriter flag must be set.

[palantirtech]

Thanks for your interest in palantir/javapoet, @pbi-qfs! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[changelog-app]

Generate changelog in changelog/@unreleased

Type (Select exactly one)

• Feature (Adding new functionality)
• Improvement (Improving existing functionality)
• Fix (Fixing an issue with existing functionality)
• Break (Creating a new major version by breaking public APIs)
• Deprecation (Removing functionality in a non-breaking way)
• Migration (Automatically moving data/functionality to a new system)

Description

Support writing Javadocs in Markdown style (JEP 467)

Check the box to generate changelog(s)

• Generate changelog entry

[pbi-qfs]

As for other pull requests for this project, anyone who has signed or is willing to sign the Palantir CLA is free to copy the code of this pull request to her or his fork and to open a new request.

[pkoenig10]

Closing in favor of #433.