Add TupleStream as new physical root operator; Move methods of value transformation to seperate class

Add googletest framework; Modify interface of parser to seperate parsing from verifying; Add parser tests

Solve bug caused when inserting with a branch not existed yet; Solve bug caused by freeing tablealias string memory to early; Solve bug concerning visibility caused by not constructing branch lineage

Add version tag recognition for update statements; Solve bug caused by not checking if tuple is visible in Tablescan operator

Add version recognition for insert statements; Add version recognition for select statements; Modify TableScan operator to store the pointer to the alias; Modify version_management to take the version of the current table; free memory after using alias

Fix bug when scanning tids with calculating the table size by summing up version_mgmt size and dangling_version_mgmt size; Iterate over full size and mark tid as dangling tid if the counter value is greater than version_mgmt size

Add sql executable as an interface for a schema free database system; Rename existing sql executable to protodb; Move database generation from query_compiler a stage above

Change return type of semantical analysis to operator instead of result; Add update operator which can be used as a node in the query tree; Fix bug with pushing up tids