Merge pull request #22 from woudshoo/mathjax-improvements

Tiny improvement, do not emit text/x-math-config script section if not n...
Minor spacing tweak to navigation.
Add and export PREVIEW.
Tweaks to injections handling. NEWS updates.
Minor tweaks to PREVIEW.
Make WRITE-PAGE overwrite existing pages by default.
Release: 0.9.1!
Raise condition if the theme package cannot be found.
Merge branch 'master' into new-theme
Merge pull request #26 from woudshoo/theme-not-exist-condition

Raise condition if the theme package cannot be found.
Minor cleanups to theme-package error handling.
Fix thinko.
Slugify tags. Fixes issue #25.
Merge remote-tracking branch 'parent/master' into new-theme