move {ARTICLE,PAGE}_DIR -> {ARTICLE,PAGE}_PATHS

Instead of one path a list can be given. This is due to popular request.
Should help people not wanting to use Pelican for blogging.
Maintain backward compatibility though.
Thanks to @ingwinlu for pointing out the change in StaticGenerator.
Fix #1344 move PLUGIN_PATH -> PLUGIN_PATHS

Pelican uses *_PATHS names for settings that represent a list of paths.
Add {PAGE,ARTICLE}_PATHS to {ARTICLE,PAGE}_EXCLUDES automatically

This makes it easier for someone to change PAGE_PATHS without the
need to change ARTICLE_EXCLUDES accordingly.
Remove AsciiDocReader from core. Fixes #1355
[coveralls] Exclude tests from coverage
Merge pull request #1376 from avaris/remove_asciidoc

Remove AsciiDocReader from core. Fixes #1355
Merge pull request #1322 from smartass101/get_files_multiple_paths

move {ARTICLE,PAGE}_DIR -> {ARTICLE,PAGE}_PATHS and correlate with {ARTICLE,PAGE}_EXCLUDES
Fix HTMLParser related deprecation warnings in Py3.4
Patch docutils.io.FileInput to not use "U" mode in py3

"U" mode is redundant in py3 since "newline" argument replaces it and by default
universal newlines is enabled. As of py3.4, "U" mode triggers a deprecation warning.