Add new fixer: TrimWhitespace (#991)

add a new fixer: trim_whitespace

autoload/ale/fix/registry.vim

@@ -57,6 +57,11 @@ let s:default_registry = {
 \       'suggested_filetypes': [],
 \       'description': 'Remove all blank lines at the end of a file.',
 \   },
+\   'trim_whitespace': {
+\       'function': 'ale#fixers#generic#TrimWhitespace',
+\       'suggested_filetypes': [],
+\       'description': 'Remove all trailing whitespace characters at the end of every line.',
+\   },
 \   'yapf': {
 \       'function': 'ale#fixers#yapf#Fix',
 \       'suggested_filetypes': ['python'],