mercurial: add editorconfig Editorconfig (http://editorconfig.org/) is a file format helping define coding styles like spaces, tabs etc. It supports a wide range of editors. Some well- known projects like ruby and zsh are using it already. This patch adds a simple .editorconfig, making it clear we use 8-char tabs in C code, 4-char spaces in Python code, and we don't keep trailing spaces.