Add .editorconfig file to help with editing in a more consistent style.

.editorconfig

+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+max_line_length = 120
+
+# 4 space indentation
+[*.{py,pyx,pxi,pxd,c,cpp}]
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = true
+
+# Tab indentation (no size specified)
+[Makefile]
+indent_style = tab
+
+# Matches the exact files either package.json or .travis.yml
+[{package.json,.travis.yml}]
+indent_style = space
+indent_size = 2