Support unusual characters in file and directory names (#868)

* Use a delimiter in node to separate file/dir name from the rest.

* Switch warning message to use nerdtree#deprecated function.

* Compress the space between the tree symbols and the node.

* Include the delimiter when calculating indent or getting filename.

* Don't need to strip leading delimiter. It will already be gone.

* Simplify the way the delimiter is being used.

I don't know what I was thinking. The delimiter doesn't need to be used
to separate every indicator on the node's text, ie.

Bad:    Tree|GenericFlags|Filename|ExecutableFlag|Link|ReadonlyFlag
Better: Tree GenericFlags|Filename|ExecutableFlag Link ReadonlyFlag

This was unnecessary, given that we're only interested in the filename.
So, just one pair of delimiters is all we need. That greatly simplifies
the _stripMarkup function, and restores a bunch of other statements to
what they already are in the master branch.

* Add syntax highlighting to conceal the delimiter

* Put a if has("conceal") check around the syntax statement using it.

* Make concealment work correctly for LinkFile and readonly files.

* Use highlight Ignore if conceal isn't available.

This is probably the best we can do, especially if some other character
must be used in place of nbsp.

* Make the regex better match the original, but more compact.

It was allowing 2+ spaces, instead of only 1+.

* Fix the syntax highlighing of delimiters around NERDTreeExecFile.

* Bug fix: Parse . and .. from path string with trailing slash.

* Fix unresponsive cascaded directories.

Using ':' as a more visible delimiter, when directories are cascaded,
the line appears in NERDTree like so:

▾ :lib/::nerdtree/:

Before this commit, the s:UI._stripMarkup function was leaving the
internal delimiters in place (lib/::nerdtree/). Now they are removed,
resulting in a valid path (lib/nerdtree/).

* Use .= to shorten statement. Use clearer substitutes to get node name.

* Remove node delimiters that terminate the line.

* If flags are needed after the node name, then put another delimiter
before them.
* When joining directory nodes for cascaded display, strip off the
delimiter from the child node(s).
* Remove the unnecessary substitution of doubled intermediate
delimiters, since they're not in there anymore.

* DRY up the addition of the 2nd delimiter, and use only 1 for all tags.

lib/nerdtree/path.vim

@@ -39,10 +39,10 @@ endfunction
 
 " FUNCTION: Path.cacheDisplayString() {{{1
 function! s:Path.cacheDisplayString() abort
-    let self.cachedDisplayString = self.getLastPathComponent(1)
+    let self.cachedDisplayString = g:NERDTreeNodeDelimiter . self.getLastPathComponent(1)
 
     if self.isExecutable
-        let self.cachedDisplayString = self.cachedDisplayString . '*'
+        let self.cachedDisplayString = self.addDelimiter(self.cachedDisplayString) . '*'
     endif
 
     let self._bookmarkNames = []
@@ -52,15 +52,24 @@ function! s:Path.cacheDisplayString() abort
         endif
     endfor
     if !empty(self._bookmarkNames) && g:NERDTreeMarkBookmarks == 1
-        let self.cachedDisplayString .= ' {' . join(self._bookmarkNames) . '}'
+        let self.cachedDisplayString = self.addDelimiter(self.cachedDisplayString) . ' {' . join(self._bookmarkNames) . '}'
     endif
 
     if self.isSymLink
-        let self.cachedDisplayString .=  ' -> ' . self.symLinkDest
+        let self.cachedDisplayString = self.addDelimiter(self.cachedDisplayString) . ' -> ' . self.symLinkDest
     endif
 
     if self.isReadOnly
-        let self.cachedDisplayString .=  ' ['.g:NERDTreeGlyphReadOnly.']'
+        let self.cachedDisplayString = self.addDelimiter(self.cachedDisplayString) . ' ['.g:NERDTreeGlyphReadOnly.']'
+    endif
+endfunction
+
+" FUNCTION: Path.addDelimiter() {{{1
+function! s:Path.addDelimiter(line)
+    if a:line =~# '\(.*' . g:NERDTreeNodeDelimiter . '\)\{2}'
+        return a:line
+    else
+        return a:line . g:NERDTreeNodeDelimiter
     endif
 endfunction