Add an .editorconfig file (and the ability to write new ones)

.editorconfig

+# ***************************
+# ** DO NOT EDIT THIS FILE **
+# ***************************
+#
+# This file was generated by edx-lint: http://github.com/edx/edx-lint
+#
+# If you want to change this file, you have two choices, depending on whether
+# you want to make a local change that applies only to this repo, or whether
+# you want to make a central change that applies to all repos using edx-lint.
+#
+# LOCAL CHANGE:
+#
+# 1. Edit the local .editorconfig_tweaks file to add changes just to this
+#    repo's file.
+#
+# 2. Run:
+#
+#       $ edx_lint write .editorconfig
+#
+# 3. This will modify the local file.  Submit a pull request to get it
+#    checked in so that others will benefit.
+#
+#
+# CENTRAL CHANGE:
+#
+# 1. Edit the .editorconfig file in the edx-lint repo at
+#    https://github.com/edx/edx-lint/blob/master/edx_lint/files/.editorconfig
+#
+# 2. Make a new version of edx_lint, which involves the usual steps of
+#    incrementing the version number, submitting and reviewing a pull
+#    request, and updating the edx-lint version reference in this repo.
+#
+# 3. Install the newer version of edx-lint.
+#
+# 4. Run:
+#
+#       $ edx_lint write .editorconfig
+#
+# 5. This will modify the local file.  Submit a pull request to get it
+#    checked in so that others will benefit.
+#
+#
+#
+#
+#
+# STAY AWAY FROM THIS FILE!
+#
+#
+#
+#
+#
+# SERIOUSLY.
+#
+# ------------------------------
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+indent_style = space
+indent_size = 4
+
+[{Makefile, *.mk}]
+indent_style = tab
+
+[{*.yml, *.yaml, *.json}]
+indent_size = 2
+
+# e2776282f95423f221b17c09c4888883be77b437

edx_lint/files/.editorconfig

+# This is a file to standardize editor settings: http://EditorConfig.org
+
+# Unix-style newlines with a newline ending every file
+# Set default charset
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+indent_style = space
+indent_size = 4
+
+# Tab indentation (no size specified)
+[{Makefile, *.mk}]
+indent_style = tab
+
+# Matches the exact files either package.json or .travis.yml
+[{*.yml, *.yaml, *.json}]
+indent_size = 2