1. [Enhancement] support all flycehck error levels.
2. New faces: doom-modeline-input-method and doom-modeline-input-method-alt.
3. [Feature] Add mouse actions to mu4e alert segment.
4. [Feature] Support two-column buffers.
5. [Enhancement] Simplify image creation: use PBM instead of XPM.
6. [Feature] Add Meow indicator.
7. [Feature] Add repl segment for CIDER.
8. Add face for notifications.
9. Be compatible with mini-frame.
10. Misc improvements.