magit-log-format-graph-function: new option

This makes it possible to implement the original proposal from #495, be
writing a single function.  Unless someone contributes that function, I
will write it myself once I find the time to do so.
magit.el: fix typo
Merge pull request #1086 from roysc/master

magit.el: fix typo
magit-key-mode: set scroll-margin to 0

Close #1087.
magit-commit-squash: unmark commit after squashing

Also add a variable magit-commit-unmark-after-squash.  But for now
do not make that an option and don't even document it.  Let's first
see if there is any demand for this being optional at all.
Run magit-run-git-bisect in the toplevel directory
Merge pull request #1091 from Silex/master

Run magit-run-git-bisect in the toplevel directory
magit-log-oneline-re: allow empty commit message
Merge pull request #1092 from dhull/feature/fix-short-log-empty-message

magit-log-oneline-re: allow empty commit message
Makefile: prevent bogus make targets

This is a kludge.  Add variable CONTRIBUTORS_URL so that no url is
lexically within the "herefile" AUTHORS_HEADER.  Otherwise https and
everything else preceding the colon would be considered a make target.
Makefile: absorb .mailmap
Makefile: use printf instead of echo
Makefile: cosmetics
Makefile: add new .mailmap rule
AUTHORS.md: update list of contributors
Merge branch 'authors'
use file-local variables instead of dir-locals.el

To not use the file `.dir-locals.el' to set buffer local variables for
Emacs lisp libraries.  Instead set `indent-tabs-mode' to nil in each
library individually.  That leads to a bit of duplication, but has the
advantage, that users can now use `.dir-locales.el' for their own
settings, without that file being tracked by git.  To make that even
more convenient tell git to ignore it.
.travis.yml: no longer allow failure on Emacs trunk
README.md: cosmetics
README.md: improve installation instructions

Point users more forcefully into the direction of Elpa and Melpa in
particular.  I am happy to provide other installation methods, but
beginners should really just setup the use of Melpa and be done with
it.