Proof concept patch version 013.  Changes include, but are not limited to:

-  The previous problem with the speed of drawing multiple fake cursors on Emacs for Windows (which occurred with patch version 012) was caused by a plethora of useful debugging messages being sent to STDERR, which caused a tremendous slow down even when launching runemacs.exe (i.e., not the terminal).  [Solution:  turn off STDERR debugging messages when not needed.]

-  Debugging messages to STDERR is now controlled by the variable mc-stderr (non-nil for ON, and nil for OFF).

-  Miscellaneous cleanup of unused variables in various functions.

-  Minor bug fixes.

-  Reorganized/grouped sections within mc_move_it [MULTIPLE_CURSORS, HORIZONTAL_RULER, VERTICAL_RULER] and added more debugging details to STDERR.

INSTALLATION:

1.  Download a current version of Emacs master branch.

2.  Reset the repository to 07/07/2018:  git reset --hard 98463bed07ecc9057094928ffdc2321eaaf3ab52

3.  Apply the attached patch from the root repository directory.

4.  Build a GUI version of Emacs:  X11, NS, or Windows.

5.  To try out built-in fake cursors with Magnar Sveen's library (multiple-cursors), install that package first.

6.  Load or evaluate the contents of crosshairs.el (attached), which includes code modifying a couple of functions used by Magnar Sveen's library.

7.  To try out the crosshairs feature, open a simple buffer (nothing fancy, just code or text) and type:  M-x +-mode

8.  To see an example of crosshairs playing nicely with tab stretches, open up something like simple.el and type:  M-x +-mode.

9.  To see an example of a variety of built-in cursor styles and widths, type:  M-x mc-test

This is still a work in progress ...