add proof of concept for path flags API and add git modified flags

lib/nerdtree/path.vim

@@ -24,6 +24,13 @@ function! s:Path.AbsolutePathFor(str)
     return toReturn
 endfunction
 
+"FUNCTION: Path.addFlag(flag) {{{1
+function! s:Path.addFlag(flag)
+    if index(self._flags, a:flag) == -1
+        call add(self._flags, a:flag)
+    endif
+endfunction
+
 "FUNCTION: Path.bookmarkNames() {{{1
 function! s:Path.bookmarkNames()
     if !exists("self._bookmarkNames")
@@ -33,8 +40,10 @@ function! s:Path.bookmarkNames()
 endfunction
 
 "FUNCTION: Path.cacheDisplayString() {{{1
-function! s:Path.cacheDisplayString()
-    let self.cachedDisplayString = self.getLastPathComponent(1)
+function! s:Path.cacheDisplayString() abort
+    let self.cachedDisplayString = self._flagString()
+
+    let self.cachedDisplayString .= self.getLastPathComponent(1)
 
     if self.isExecutable
         let self.cachedDisplayString = self.cachedDisplayString . '*'
@@ -350,6 +359,15 @@ function! s:Path.getSortOrderIndex()
     return s:NERDTreeSortStarIndex
 endfunction
 
+"FUNCTION: Path._flagString() {{{1
+function! s:Path._flagString()
+    if empty(self._flags)
+        return ""
+    endif
+
+    return '[' . join(self._flags, ',') . ']'
+endfunction
+
 "FUNCTION: Path.isUnixHiddenFile() {{{1
 "check for unix hidden files
 function! s:Path.isUnixHiddenFile()
@@ -460,6 +478,7 @@ function! s:Path.New(path)
     call newPath.readInfoFromDisk(s:Path.AbsolutePathFor(a:path))
 
     let newPath.cachedDisplayString = ""
+    let newPath._flags = []
 
     return newPath
 endfunction
@@ -480,6 +499,14 @@ function! s:Path.Resolve(path)
     return tmp =~# '.\+/$' ? substitute(tmp, '/$', '', '') : tmp
 endfunction
 
+"FUNCTION: Path.removeFlag(flag) {{{1
+function! s:Path.removeFlag(flag)
+    let i = index(self._flags, a:flag)
+    if i >= 0
+        call remove(self._flags, i)
+    endif
+endfunction
+
 "FUNCTION: Path.readInfoFromDisk(fullpath) {{{1
 "
 "
@@ -537,6 +564,7 @@ endfunction
 "FUNCTION: Path.refresh() {{{1
 function! s:Path.refresh()
     call self.readInfoFromDisk(self.str())
+    call g:NERDTreeRefreshNotifier.NotifyListeners(self)
     call self.cacheDisplayString()
 endfunction