mu4e: update documentation with some examples
mu4e: add mu4e-headers-find-if

This function can be used to jump to some message in the headers list
that matches a certain pattern.
mu4e: update mu4e-headers-find-if documentation
Add documentation about mu4e-compose-dont-reply-to-self
Merge pull request #518 from zakkak/docUpdate

mu4e: Add documentation about mu4e-compose-dont-reply-to-self
mu4e-shr2text does not anymore retrieve images.

When HTML emails contain references to remote images, retrieving these images
leaks informationo.  For example, the sender can see when I openend the email
and from which computer (IP address).  For this reason, it is preferrable to
not retrieve images.
Merge branch 'master' of github.com:djcb/mu