Import .editorconfig from PostgreSQL

This is the very same .editorconfig file that PostgreSQL is using.

postgres/postgres@ecb09cd

Author: df7cb

.editorconfig

@@ -0,0 +1,14 @@
+root = true
+
+[*.{c,h,l,y,pl,pm}]
+indent_style = tab
+indent_size = tab
+tab_width = 4
+
+[*.{sgml,xml}]
+indent_style = space
+indent_size = 1
+
+[*.xsl]
+indent_style = space
+indent_size = 2