Treat dot files and folders same as internal

[abelsromero]

Thank you for opening a pull request and contributing to asciidoctor-maven-plugin!

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Documentation
• Refactor
• Build improvement
• Other (please describe)

What is the goal of this pull request?
Seeing the recent light of an issue with internal files treatment #545 we have been able to spot similar issues with treatment of hidden (prefix "." files and directories).
For that reason I think it's reasonable the next changes:

• FIX: In v2.1.0 sources inside a hidden directory where not processed, but they are in 2.2.x
• FEATURE CHANGE: While in v2.1.0 resources folders with "." where copied, it's not consistent with sources and internal resources (""). So this PR applies same treatment as with "" and aligns it with "." sources which are also ignored.

Are there any alternative ways to implement this?
We could have left behauviour as in 2.1.0 and copy "." folders, but that's an odd case not consistent with the rest.

Are there any implications of this pull request? Anything a user must know?
Users having resources in hidden folders "." will need to rename them.
This could impact Windows users that do not follow Unix "hidden" files conventions, but I struggle to argue using this naming is a good practice we want to promote.

Is it related to an existing issue?

• Yes
• No

Finally, please add a corresponding entry to CHANGELOG.adoc

[uniqueck]

Would you like to setup a invoker test or is that enough to cover this behaviour with normal module tests?

[abelsromero]

I think this is should be enough. In fact one of the things I'd like to try for next 3.0.0 is refactor the code into more decoupled pieces and do a more unit test approach like in this case.
Most of the tests are in fact integration tests that rely on full asciidoctorj conversions and that adds slowness and complexity.

...but this is of course open to discussion.