Add support for OUTPUT_DIR_IGNORE setting.

Fixes issue #66.
PEP8 changes.
Fix up PyCharm inspection/style settings and fix some minor formatting issues.
Add .gitattributes for line ending normalization.

Unfortunately there are some files that aren't properly normalized
in the repo for whatever reason, so this commit is ugly. Hopefully this
resolves the issue for the future.
Remove Tweet submodule.
Remove Tweet-related settings and theme content.

Fixes #65.
Add setting to force metadata fencing for all posts.