Fix typo
Merge pull request #203 from purcell/patch-2

* fix typo
* mu4e: fix typo
* merge branch 'master' of github.com:djcb/mu
* lib: update comment
* cosmetic
* mu: improve cfind help text
* cosmetic
* mu4e: correctly apply 'trashed' face (headers); make face selection a bit more explicit
* mu4e: fix header shrinking/growing