Merge pull request #825 from avaris/markdown-summary

fix for issue #761: handle unicode correctly in summary for Markdown
Fix for issue #428: Use PLUGIN_PATH properly
Merge pull request #828 from avaris/plugin-path

Fix for issue #428: Use PLUGIN_PATH properly
Add translation metadata support.

Allows user to control which posts are the translations independently of the
DEFAULT_LANG setting.
Minor English grammar correction
Merge pull request #830 from Rogdham/translation_metadata

Add translation metadata support.
Merge branch 'master' into 3.3-tests