this is because of vims fucking stupid functionality where ignorecase
changes the way == behaves. It was causing bugs when the user had
ignorecase set.

now we can go   vim  <some dir>   and it loads up a nerd tree instead of
a netrw

when the user activate the   ../ (up a dir)   line or hit U or U it
wasnt changing vims CWD when NERDTreeChDirMode==2

allows the statusline to be customised for the nerd tree window

Path.New was expecting an absolute path. Now we convert paths to
absolute inside Path.New

make sure we always go back to the right buffer, and if there is no
buffer to go back to, close the window

since we are now ":edit"ing a new buffer for secondary nerd trees, we
have to store the previous buffer number otherwise we get into an
infinite loop because we go back to a directory buffer which causes
another secondary nerd tree to open etc

if we were using e on the current dir (or a file in that dir) then we
would end up doing an ":edit" with no target. Now we use "." in
Path#strForEditCmd if it would resolve to an empty string

Use a sequential numbering system instead of timestamps. This makes the
buffer names shorter and neater and easier on the eye when using
:NERDTreeMirror

remove "top" and "bottom" as valid settings for NERDTreeWinPos