Add WP_Error namespace and no title default title

[ravichdev]

Summary

Fixes #13

Checklist

• My pull request is addressing an open issue (please create one otherwise).
• My code is tested and passes existing tests.
• My code follows the Contributing Guidelines (updates are often made to the guidelines, check it out periodically).

[coveralls]

Pull Request Test Coverage Report for Build 742323636

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.1%) to 84.657%

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Totals
Change from base Build 730264630:	1.1%
Covered Lines:	3741
Relevant Lines:	4358

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💛 - Coveralls