Feature/stream transactions (#292)

* beginStreamTransaction

* abortStreamTransaction

* differentiated tests for aborting invalidTransactionId and notExistingTransactionId

* getStreamTransaction

* formatted code adopting project formatter

* requireVersion 3.5 for Stream Transaction tests

* commitStreamTransaction

* bugfix requireVersion using assumeTrue

* ArangoDatabase::getEngine

* requireStorageEngine rocksdb for stream transaction tests

* stream transactions extension for document and collection APIs

* test commitStreamTransactionTwice and abortStreamTransactionTwice

* Stream Transactions collections operations test

* stream transactions: replaceDocument & replaceDocuments test

* stream transactions: test

* stream transactions: test

* stream transactions: Cursors

* authorship comments

* stream transactions: moved all tests together

* @SInCE comments

* ConcurrentStreamTransactionsTest

* stream transactions: skip tests for cluster environments

* stream transactions: test operation with invalid tx id

Author: rashtao

ChangeLog.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ### Added
 
+- added support for Stream Transactions
 - added support for named indices
 - added support for TTL indices
 - added minReplicationAttribute for collections and graphs