Remove trailing whitespaces

[etanot]

This commit contains following changes:

• Remove trailing whitespaces.
  Usually, we don't want to have trailing whitespaces at the end of
  line. It makes diff uglier and maintenance of code harder.
• Replace non-breaking whitespace with simple whitespace.
  Like trailing whitespaces, we also don't want to have non-breaking
  whitespace1 in our source files.

[kushaldas]

Many of these whitespaces are from command output pasting, if we remove them, it will be a trouble for everytime we update those outputs. In my mind I am okay to keep those.

[etanot]

If you want, I can drop changes which contains commands output. But IMHO, a good solution would be to never have these changes at the first place. We could configure our text editor display different non-printable characters and automatically clean them on pressing some key bindings. For example, in Vim, I've added following code snippet to my vimrc file to display different non-printable characters:

" ======= Display non-printable characters =======
set list
set listchars=eol:⏎
set listchars+=extends:❯
set listchars+=nbsp:⍽
set listchars+=precedes:❮
set listchars+=tab:⇥‧
set listchars+=trail:◦
" ==============================================

and defined a function to remove trailing whitespaces:

" Remove trailing whitespace(s) and replace non-breaking whitespace
" character(s) with whitespace on save, useful for some filetypes.

function! CleanFiles#CleanWhitespaces()
    let save_cursor = getpos(".")
    let old_query = getreg('/')

    " Remove trailing whitespace(s).
    silent! %s/\s\+$//e

    " Replace non-breaking whitespace character(s) with whitespace.
    silent! %s/\%u00a0/ /e

    call setpos('.', save_cursor)
    call setreg('/', old_query)
endfunction