add splay_tree.md file

Author: eulerkochy

docs/src/splay_tree.md

@@ -0,0 +1,34 @@
+```@meta
+DocTestSetup = :(using DataStructures)
+```
+
+# Splay Tree
+
+The `SplayTree` type is an implementation of Splay Tree in Julia. It is a self-balancing binary search tree with the additional property that recently accessed elements are quick to access again. Operations such as search, insert and delete can be done in `O(log n)` amortized time, where `n` is the number of nodes in the `SplayTree`.
+
+Examples:
+
+```jldoctest
+julia> tree = SplayTree{Int}();
+
+julia> for k in 1:2:20
+           push!(tree, k)
+       end
+
+julia> haskey(tree, 3)
+true
+
+julia> tree[4]
+7
+
+julia> for k in 1:2:10
+           delete!(tree, k)
+       end
+
+julia> haskey(tree, 5)
+false
+```
+
+```@meta
+DocTestSetup = nothing
+```