editorconfig: add indentation rules

Commands used to list the file extensions used in the project:

    $ git ls-files | sed -En 's/.*(\.[^.]+)$/\1/p' |
      LC_ALL=C sort | uniq -c

For rules that are more specific to a given directory, put a dedicated
.editorconfig file in it.

.editorconfig

@@ -5,3 +5,30 @@ charset = utf-8
 end_of_line = lf
 insert_final_newline = true
 trim_trailing_whitespace = true
+
+# Build
+[configure.ac]
+indent_size = 8
+indent_style = tab
+
+[*{.mk,Makefile}{,.in}]
+indent_size = 8
+indent_style = tab
+
+# Source code and scripts
+[*.{c,h}{,.in}]
+indent_size = 8
+indent_style = tab
+
+[*.{awk,exp,sh}{,.in}]
+indent_size = 8
+indent_style = tab
+
+[*.py{,.in}]
+indent_size = 4
+indent_style = space
+
+# Misc
+[.gitlab-ci.yml]
+indent_size = 4
+indent_style = space

.github/.editorconfig

@@ -0,0 +1,3 @@
+[*.yml]
+indent_size = 2
+indent_style = space

contrib/syntax/.editorconfig

@@ -0,0 +1,7 @@
+[*.lang{,.in}]
+indent_size = 2
+indent_style = space
+
+[*.vim{,.in}]
+indent_size = 2
+indent_style = space

platform/rpm/.editorconfig

@@ -0,0 +1,3 @@
+[*.sh{,.in}]
+indent_size = 4
+indent_style = space

src/bash_completion/.editorconfig

@@ -0,0 +1,3 @@
+[*.bash_completion{,.in}]
+indent_size = 4
+indent_style = space

src/zsh_completion/.editorconfig

@@ -0,0 +1,3 @@
+[_*{,.in}]
+indent_size = 4
+indent_style = space