Add .editorconfig file to simplify editing and reading the source files
The libxml2 sources unfortunately contains a mix of space and tab based indentation.
If this should be remedied is a separate issue.
To avoid the matters getting worse an .editorconfig file could be used.
Most editors handle .editorconfig either natively or through extensions.
A basic setup could contain:
# EditorConfig : http://EditorConfig.org
# top-most EditorConfig file
root = true
[Makefile]
indent_style = tab
[CMakeLists.txt]
indent_style = tab
indent_size = 4
[*.{c,h}]
indent_style = space
indent_size = 4