C++ - better => butter

Summary:
Renaming the `better` utilities to `butter`:
- to prevent claims that this library is superior to others - it really depends on use cases
- to indicate ease of use throughout the codebase, easily spread like butter

Changelog: [C++][Changed] Renaming C++ better util to butter, used by Fabric internals

Reviewed By: JoshuaGross

Differential Revision: D33242764

fbshipit-source-id: 26dc95d9597c61ce8e66708e44ed545e0fc5cff5

ReactCommon/react/utils/SimpleThreadSafeCache.h

@@ -9,7 +9,7 @@
 #include <memory>
 #include <mutex>
 
-#include <better/optional.h>
+#include <butter/optional.h>
 #include <folly/container/EvictingCacheMap.h>
 
 namespace facebook {
@@ -48,7 +48,7 @@ class SimpleThreadSafeCache {
    * If the value wasn't found in the cache, returns empty optional.
    * Can be called from any thread.
    */
-  better::optional<ValueT> get(const KeyT &key) const {
+  butter::optional<ValueT> get(const KeyT &key) const {
     std::lock_guard<std::mutex> lock(mutex_);
     auto iterator = map_.find(key);
     if (iterator == map_.end()) {