Add Next And Previous Floats as a ruby til.

ruby/next-and-previous-floats.md

@@ -0,0 +1,38 @@
+# Next And Previous Floats
+
+The `Float` class has two interesting methods for stepping forward or
+backwards through the numbers that can actually be *represented* by floats.
+This is handy since floats are not evenly spaced.
+
+Use `#next_float` to go forward
+
+```ruby
+> 2.0
+=> 2.0
+> _.next_float
+=> 2.0000000000000004
+> _.next_float
+=> 2.000000000000001
+> _.next_float
+=> 2.0000000000000013
+> _.next_float
+=> 2.0000000000000018
+```
+
+Use `#prev_float` to go backwards
+
+```ruby
+> 2.0
+=> 2.0
+> _.prev_float
+=> 1.9999999999999998
+> _.prev_float
+=> 1.9999999999999996
+> _.prev_float
+=> 1.9999999999999993
+> _.prev_float
+=> 1.9999999999999991
+```
+
+I cannot think of any practical use cases, but it is fun to know they are
+there if you need them.