Fixes to 1993/ejb

Rename ejb.explain[12] files to their respective markdown files with the
name of the puzzle they explain.

Fix formatting of README.md.

1993/ejb/hanoi.md

@@ -0,0 +1,11 @@
+# The Towers of Hanoi puzzle
+
+The Towers of Hanoi is a puzzle consisting of three posts
+and several rings of various sizes.  The initial
+configuration of the game is that all the rings are stacked
+in decreasing order of size on one post.  The object of the
+game is to move all the rings from one post to another
+subject to two rules: only one ring can be moved at a time,
+and at no time can one ring be placed on top of a smaller
+ring.  The number of steps necessary to solve this puzzle is
+exponential in the number rings.