boilerplate: add .dir-locals.el with emacs python enviroment

The .dir-locals.el set the project's python enviroment for the emacs tasks like
flycheck or jedi.  The py-environment has to be next to <repo>/.dir-locals.el::

    ./local/py3

To setup such an environment build target 'pyenv' or 'pyenvinstall'::

  $ make pyenvinstall

TL;DR

Alternatively create the virtualenv, source it and install jedi + epc
(required by `emacs-jedi <https://tkf.github.io/emacs-jedi>`_)::

    $ virtualenv --python=python3  "--no-site-packages" ./local/py3
    ...
    $ source ./local/py3/bin/activate
    (py3)$ # now install into the activated 'py3' environment ..
    (py3)$ pip install jedi epc
    ...

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

.dir-locals.el

@@ -0,0 +1,117 @@
+;;; .dir-locals.el
+;;
+;; If you get ``*** EPC Error ***`` with this setup in your emacs session,
+;; mostly you have jedi-mode enabled but the python enviroment is missed.  The
+;; python environment has to be next to the ``<repo>/.dir-locals.el`` in::
+;;
+;;    ./local/py3
+;;
+;; In Emacs, some buffer locals are referencing the project environment:
+;;
+;; - prj-root                                --> <repo>/
+;; - python-environment-directory            --> <repo>/local
+;; - python-environment-default-root-name    --> py3
+;; - python-shell-virtualenv-root            --> <repo>/local/py3
+;;       When this variable is set with the path of the virtualenv to use,
+;;      `process-environment' and `exec-path' get proper values in order to run
+;;      shells inside the specified virtualenv, example::
+;;         (setq python-shell-virtualenv-root "/path/to/env/")
+;;
+;; To setup such an environment build target 'pyenv' or 'pyenvinstall'::
+;;
+;;   $ make pyenvinstall
+;;
+;; Alternatively create the virtualenv, source it and install jedi + epc
+;; (required by `emacs-jedi <https://tkf.github.io/emacs-jedi>`_)::
+;;
+;;     $ virtualenv --python=python3  "--no-site-packages" ./local/py3
+;;     ...
+;;     $ source ./local/py3/bin/activate
+;;     (py3)$ # now install into the activated 'py3' environment ..
+;;     (py3)$ pip install jedi epc
+;;     ...
+
+((nil
+  . ((fill-column . 80)
+     ))
+ (python-mode
+  . ((indent-tabs-mode . nil)
+
+     ;; project root folder is where the `.dir-locals.el' is located
+     (eval . (setq-local
+	      prj-root (locate-dominating-file  default-directory ".dir-locals.el")))
+
+     (eval . (setq-local
+	      python-environment-directory (expand-file-name "./local" prj-root)))
+
+     ;; use 'py3' enviroment as default
+     (eval . (setq-local
+	      python-environment-default-root-name "py3"))
+
+     (eval . (setq-local
+	      python-shell-virtualenv-root
+	      (concat python-environment-directory
+		      "/"
+		      python-environment-default-root-name)))
+
+     ;; python-shell-virtualenv-path is obsolete, use python-shell-virtualenv-root!
+     ;; (eval . (setq-local
+     ;; 	 python-shell-virtualenv-path python-shell-virtualenv-root))
+
+     (eval . (setq-local
+	      python-shell-interpreter
+	      (expand-file-name "bin/python" python-shell-virtualenv-root)))
+
+     (eval . (setq-local
+	      python-environment-virtualenv
+	      (list (expand-file-name "bin/virtualenv" python-shell-virtualenv-root)
+		    ;;"--system-site-packages"
+		    "--quiet")))
+
+     (eval . (setq-local
+	      pylint-command
+	      (expand-file-name "bin/pylint" python-shell-virtualenv-root)))
+
+     ;; pylint will find the '.pylintrc' file next to the CWD
+     ;;   https://pylint.readthedocs.io/en/latest/user_guide/run.html#command-line-options
+     (eval . (setq-local
+	      flycheck-pylintrc ".pylintrc"))
+
+     ;; flycheck & other python stuff should use the local py3 environment
+     (eval . (setq-local
+	      flycheck-python-pylint-executable python-shell-interpreter))
+
+     ;; use 'M-x jedi:show-setup-info'  and 'M-x epc:controller' to inspect jedi server
+
+     ;; https://tkf.github.io/emacs-jedi/latest/#jedi:environment-root -- You
+     ;; can specify a full path instead of a name (relative path). In that case,
+     ;; python-environment-directory is ignored and Python virtual environment
+     ;; is created at the specified path.
+     (eval . (setq-local  jedi:environment-root  python-shell-virtualenv-root))
+
+     ;; https://tkf.github.io/emacs-jedi/latest/#jedi:server-command
+     (eval .(setq-local
+	     jedi:server-command
+	     (list python-shell-interpreter
+		   jedi:server-script)
+	     ))
+
+     ;; jedi:environment-virtualenv --> see above 'python-environment-virtualenv'
+     ;; is set buffer local! No need to setup jedi:environment-virtualenv:
+     ;;
+     ;;    Virtualenv command to use.  A list of string.  If it is nil,
+     ;;    python-environment-virtualenv is used instead.  You must set non-nil
+     ;;    value to jedi:environment-root in order to make this setting work.
+     ;;
+     ;;    https://tkf.github.io/emacs-jedi/latest/#jedi:environment-virtualenv
+     ;;
+     ;; (eval . (setq-local
+     ;; 	      jedi:environment-virtualenv
+     ;; 	      (list (expand-file-name "bin/virtualenv" python-shell-virtualenv-root)
+     ;; 		    ;;"--python"
+     ;; 		    ;;"/usr/bin/python3.4"
+     ;; 		    )))
+
+     ;; jedi:server-args
+
+     )))