add missing LICENSE and README file from vendored libs

vendor/github.com/petar/GoLLRB/LICENSE

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+Copyright (c) 2010, Petar Maymounkov
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+(*) Redistributions of source code must retain the above copyright notice, this list
+of conditions and the following disclaimer.
+
+(*) Redistributions in binary form must reproduce the above copyright notice, this
+list of conditions and the following disclaimer in the documentation and/or
+other materials provided with the distribution.
+
+(*) Neither the name of Petar Maymounkov nor the names of its contributors may be
+used to endorse or promote products derived from this software without specific
+prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/github.com/petar/GoLLRB/README.md

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+# GoLLRB
+
+GoLLRB is a Left-Leaning Red-Black (LLRB) implementation of 2-3 balanced binary
+search trees in Go Language.
+
+## Overview
+
+As of this writing and to the best of the author's knowledge, 
+Go still does not have a balanced binary search tree (BBST) data structure.
+These data structures are quite useful in a variety of cases. A BBST maintains
+elements in sorted order under dynamic updates (inserts and deletes) and can
+support various order-specific queries. Furthermore, in practice one often
+implements other common data structures like Priority Queues, using BBST's.
+
+2-3 trees (a type of BBST's), as well as the runtime-similar 2-3-4 trees, are
+the de facto standard BBST algoritms found in implementations of Python, Java,
+and other libraries. The LLRB method of implementing 2-3 trees is a recent
+improvement over the traditional implementation. The LLRB approach was
+discovered relatively recently (in 2008) by Robert Sedgewick of Princeton
+University.
+
+GoLLRB is a Go implementation of LLRB 2-3 trees.
+
+## Maturity
+
+GoLLRB has been used in some pretty heavy-weight machine learning tasks over many gigabytes of data.
+I consider it to be in stable, perhaps even production, shape. There are no known bugs.
+
+## Installation
+
+With a healthy Go Language installed, simply run `go get github.com/petar/GoLLRB/llrb`
+
+## Example
+    
+	package main
+
+	import (
+		"fmt"
+		"github.com/petar/GoLLRB/llrb"
+	)
+
+	func lessInt(a, b interface{}) bool { return a.(int) < b.(int) }
+
+	func main() {
+		tree := llrb.New(lessInt)
+		tree.ReplaceOrInsert(1)
+		tree.ReplaceOrInsert(2)
+		tree.ReplaceOrInsert(3)
+		tree.ReplaceOrInsert(4)
+		tree.DeleteMin()
+		tree.Delete(4)
+		c := tree.IterAscend()
+		for {
+			u := <-c
+			if u == nil {
+				break
+			}
+			fmt.Printf("%d\n", int(u.(int)))
+		}
+	}
+
+## About
+
+GoLLRB was written by [Petar Maymounkov](http://pdos.csail.mit.edu/~petar/). 
+
+Follow me on [Twitter @maymounkov](http://www.twitter.com/maymounkov)!