Enable full path specifications for NERDTreeIgnore (#1207)

* Add ability to specify a path to be ignored.

This ignore expression compares itself against the whole path of the
node, instead of just the tail component of the node.

* Remove debug statements and make it work on Windows.

* Restore the original self.str() to get OS-specific paths for comparing.

Using the UI-formatted path had two problems.
1. It always appended a forward slash at the end of the path, which was
   unnecessary and made patterns like '/tmp/cache$[[path]]' not work as
   expected.
2. It always used forward slashes to join the path components. I thought
   this would be a good thing, but there's no reason to force Windows
   users to use that syntax. They'll just need to remember to escape the
   backslashes, like so: '\\Temp\\cache$[[path]]'

* Add documentation for the new [[path]] tag for NERDTreeIgnore.

* Replace the abbreviation 'dir' with the full word 'directory'.

* Update version number in change log.

CHANGELOG.md

@@ -4,6 +4,8 @@
      version in an unordered list.  The format is:
         - **.PATCH**: Pull Request Title (PR Author) [PR Number](Link to PR)
 -->
+#### 6.10
+- **.0**: Enable full path specifications for NERDTreeIgnore (PhilRunninger) [#1207](https://github.com/preservim/nerdtree/pull/1207)
 #### 6.9
 - **.12**: Respect NERDTreeCustomOpenArgs when opening bookmark (przepompownia) [#1200](https://github.com/preservim/nerdtree/pull/1200)
 - **.11**: Revamp the README. (buncis, PhilRunninger) [#1192](https://github.com/preservim/nerdtree/pull/1192), [#1193](https://github.com/preservim/nerdtree/pull/1193)