adds cmake-format config from xt-common

.cmake_format.py

+# ~~~
+# This file is part of the dune-xt-common project:
+#   https://github.com/dune-community/dune-xt-common
+# Copyright 2009-2018 dune-xt-common developers and contributors. All rights reserved.
+# License: Dual licensed as BSD 2-Clause License (http://opensource.org/licenses/BSD-2-Clause)
+# Authors:
+#   Rene Milk (2018)
+#
+# How wide to allow formatted cmake files
+# ~~~
+
+line_width = 119
+
+# How many spaces to tab for indent
+tab_size = 2
+
+# If arglists are longer than this, break them always
+max_subargs_per_line = 3
+
+# If true, separate flow control names from their parentheses with a space
+separate_ctrl_name_with_space = False
+
+# If true, separate function names from parentheses with a space
+separate_fn_name_with_space = False
+
+# If a statement is wrapped to more than one line, than dangle the closing
+# parenthesis on it's own line
+dangle_parens = False
+
+# What character to use for bulleted lists
+bullet_char = '*'
+
+# What character to use as punctuation after numerals in an enumerated list
+enum_char = '.'
+
+# What style line endings to use in the output.
+line_ending = 'unix'
+
+# Format command names with this case. Options are "lower", "upper",
+# "unchanged"
+command_case = u'lower'