Add vim setting to not leave whitespace after backslash

Should avoid problem in #207,
but should it be the default?

autoload/sj/vim.vim

@@ -8,7 +8,12 @@ function! sj#vim#Split()
   if sj#BlankString(new_line)
     return 0
   else
-    let new_line = "\n\\ ".sj#Trim(new_line)
+    if sj#settings#Read('vim_split_whitespace_after_backslash')
+      let new_line = "\n\\ ".sj#Trim(new_line)
+    else
+      let new_line = "\n\\".sj#Trim(new_line)
+    endif
+
     call sj#ReplaceMotion('vg_', new_line)
     call sj#Keeppatterns('s/\s\+$//e')
 

plugin/splitjoin.vim

@@ -37,6 +37,7 @@ let g:splitjoin_default_settings = {
       \ 'html_attribute_bracket_on_new_line':      0,
       \ 'java_argument_split_first_newline':       0,
       \ 'java_argument_split_last_newline':        0,
+      \ 'vim_split_whitespace_after_backslash':    1,
       \ }
 
 if !exists('g:splitjoin_join_mapping')

spec/plugin/vim_spec.rb

@@ -8,6 +8,10 @@
     vim.set 'shiftwidth', 2
   end
 
+  after :each do
+    vim.command('silent! unlet g:splitjoin_vim_split_whitespace_after_backslash')
+  end
+
   specify ":if commands" do
     contents = <<~EOF
       if condition == 1
@@ -23,4 +27,46 @@
     split
     assert_file_contents contents
   end
+
+  specify "backslashes" do
+    set_file_contents <<~EOF
+      let foo = 2 + 2
+    EOF
+
+    vim.search('+')
+    split
+
+    assert_file_contents <<~EOF
+      let foo = 2
+            \\ + 2
+    EOF
+
+    join
+
+    assert_file_contents <<~EOF
+      let foo = 2 + 2
+    EOF
+  end
+
+  specify "backslashes without a space" do
+    vim.command('let g:splitjoin_vim_split_whitespace_after_backslash = 0')
+
+    set_file_contents <<~EOF
+      let foo = 2 + 2
+    EOF
+
+    vim.search('+')
+    split
+
+    assert_file_contents <<~EOF
+      let foo = 2
+            \\+ 2
+    EOF
+
+    join
+
+    assert_file_contents <<~EOF
+      let foo = 2 + 2
+    EOF
+  end
 end