mu4e: small doc update
mu4e: propertize the colon in view header keys
mu4e: propertize parens around attachment size in message view
mu4e: add custom variable for list of visible flags to display in headers view
Merge pull request #141 from abend/master

* some visual improvements
* revert "mu4e: add custom variable for list of visible flags to display in headers view"

This reverts commit 9944a4fd62cb96c0ad350e991ea62fb2889703cd.