* Define default values for new variables governing new "Default Open".
"Default Open" means to open a file with the Enter key (which of course
can be changed.) The key can be changed in the vimrc, and there is a
variable for specifying the Opener parameters for opening the node. This
lets the user decide whether Enter (or another key) will open a file in
the current tab or a new one, and whether or not to open the file again
in the tab or jump to a window where the file is already open.
* Remove the old mapping for <CR>, a duplicate of 'o'.
<CR> will be defined like all the other keys, in plugin/NERD_tree.vim
* Assign functions to the new <CR> key mapping.
Three separate functions handle directories, files, and bookmarks.
* Rename variables: NERDTreeCustomOpen and NERDTreeCustomOpenArgs
* Add documentation for NERDTreeCustomOpenArgs and NERDTree-<CR>.
* Make key mapping variables be indexed in the Vim help
* Remove angle brackets from <CR> to see if help navigation improves.
* Rename functions from defaultOpen... to customOpen...
* Use separate options for file and directory nodes.
* Update documentation for separate file/directory options.
* Update version number and change log.
* Change CR to <CR> in help tags.
* Fix missing backtick in patch number.
* Update the quickhelp text.
* Update Pull Request template.
* Update change log with simpler formatting of patch number.
* Get NERDTree version number directly from CHANGELOG.md
* Reformat the lists of contributors in the Change Log.
* Initialize the version text, just in case the while loop finds nothing.
* Update CHANGELOG and change it to Markdown format.
* Add PR template with checklist for advancing the version number.
* Update version number.
* Change PR number in change log and PR template.
