Zenburn for Emacs 2.7

New features

• #347: Add support for highlight-symbol and highlight-thing.
• Add helm-lxc support.
• Theme swiper-line-face and swiper-isearch-current-match.
• #330: Add centaur-tabs, doom-modeline, and solaire-mode support.
• Add notmuch support

Changes

• #346: Make numbers in highlight-numbers blue.
• Make zenburn-add-font-lock-keywords customizable.

Bugs fixed

• #321: Scale org-document-title only if zenburn-scale-org-headlines is t.
• Fix lots of face inheritance issues on Emacs 27.