cmake, tests: enable_testing() and add_test() added to cmake
tests: ctest check during debian and rhel build added
benchmark: Simple benchmarks for deep and flat tree added
tests: actions_set suite name fixed
utils: Function to print rapidjson value moved to utils.hpp
aggregator: basic aggregation tools added

- Aggregator is a concept for collecting call trees provided by react
- aggregator_t is an interface that can collect call_tree and produce
  json report about aggregated data
tests: simple aggregator test added
docs: code_is_valid method doxygen description added
aggregators: Aggregators are moved into separate folder, paths changed
copyrights: Copyrights added to aggregators
aggregator: unordered_call_tree refactoring

- unordered_call_tree moved out from call_tree.hpp to loose coupling in
  system. Now call_tree is not dependent on it
- unordered_call_tree_aggregator added. It merges aggregated trees into
  one unordered_call_tree
- in examples unordered_call_tree replaced with aggregator
tests, aggregators: unordered_call_tree_aggregator test added
core: merge_into for merging call_tree into call_tree added
api, aggregators: react_activate now takes aggregator as parameter

In order to collect traces from react, aggregator is passed into
react_activate function. All results of react tracing will be aggregated
using this aggregator.
api, aggregators: Aggregator is passed as void* to react_activate now