Add the vimtutor shell script

This is the exact same vimtutor from the vim source repository:

  https://vim.googlecode.com/hg/src/vimtutor

It works as is in MSYS, although there are a couple of warnings:

  /bin/vimtutor: line 28: mktemp: command not found
  /bin/vimtutor: line 28: tempfile: command not found

Since these utilities are not present.

However, the script has a contingency for that scenario, and manages to
create a temporary copy of the tutor file anyway, so all is well.

Signed-off-by: Curtis Rueden <ctrueden@wisc.edu>
vimtutor: avoid warning due to Windows' lack of mktemp

This is the quickest way to avoid those warnings, and this developer deems
that good enough a work around.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
copy-files.sh: ship the vim tutor files

This copies the vimtutor shell script, along with all the vim tutor
files themselves in various languages, into the Git for Windows
distribution.

Since vi(m) is Git's default editor, and vi(m) has a steep learning
curve, shipping the vimtutor will help mitigate some of that difficulty
for new users. After all, they have enough on their plates learning Git,
without being stuck in an editor they do not know how to control, too!

Fixes issue #217.

Signed-off-by: Curtis Rueden <ctrueden@wisc.edu>
Merge pull request #220 from ctrueden/vimtutor

This adds the vimtutor script to help new users with vi, since it
is still our default editor.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>