Add fixer tidy for HTML

Add tests for tidy HTML fixer

autoload/ale/fix/registry.vim

@@ -22,6 +22,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['python'],
 \       'description': 'Fix PEP8 issues with black.',
 \   },
+\   'tidy': {
+\       'function': 'ale#fixers#tidy#Fix',
+\       'suggested_filetypes': ['html'],
+\       'description': 'Fix HTML files with tidy.',
+\   },
 \   'prettier_standard': {
 \       'function': 'ale#fixers#prettier_standard#Fix',
 \       'suggested_filetypes': ['javascript'],