Make the behavior of window splits consistent (#1035)

* add option to spawn split from previous window

* Update some comments and remove debugging statement.

* Simplify the code, and make it respect NERDTreeWinPos and 'splitbelow'.

* Better logic for getting NERDTree window number when not active window.

* Use common functions for splitting windows. Make splitting respect user.

The placement of split windows now respects the user's choices for the
splitright and splitbelow settings, and the g:NERDTreeWinPos variable.

* Update version number in change log.

autoload/nerdtree.vim

@@ -4,6 +4,11 @@ endif
 let g:loaded_nerdtree_autoload = 1
 
 let s:rootNERDTreePath = resolve(expand("<sfile>:p:h:h"))
+
+"FUNCTION: nerdtree#version(...) {{{1
+"  If any value is given as an argument, the entire line of text from the
+"  change log is shown for the current version; otherwise, only the version
+"  number is shown.
 function! nerdtree#version(...)
     let l:changelog = readfile(join([s:rootNERDTreePath, "CHANGELOG.md"], nerdtree#slash()))
     let l:text = 'Unknown'
@@ -22,6 +27,7 @@ endfunction
 " SECTION: General Functions {{{1
 "============================================================
 
+"FUNCTION: nerdtree#slash() {{{2
 function! nerdtree#slash()
 
     if nerdtree#runningWindows()
@@ -49,7 +55,6 @@ function! nerdtree#and(x,y)
             if (l:x % 2) && (l:y % 2)
                 let l:result += float2nr(pow(2, l:n))
             endif
-            echomsg l:x . ", " . l:y . " => " l:result
             let l:x = float2nr(l:x / 2)
             let l:y = float2nr(l:y / 2)
             let l:n += 1