engine: implement engine

[tpdenk]

Implement an engine that can execute our IR.

Scope:

• define file format (engine: define file format for the database files #178)
• implement support for file format (engine: implement support for file format #180)
• add high level profiling (engine: high level profiling #181)
• add integration tests (engine: integration tests #182)
• add benchmarks (engine: add microbenchmarks #183)
• add documentation documents