Fix memory leak with callbacktimer
Enforcing coding style
Use const and std::move in some places
Initial GTest support added

Minor changes on CMakeLists to add Google Test support. A new directory
tests was created to store unit test files. A basic test was added too as
reference. Code coverage will be added in the future.
Add thread pool to decode messages and websockets
Merge branch 'master' of github.com:foolano/miniriemann
Merge branch 'thread_pool'

Conflicts:
	CMakeLists.txt
	tests/CMakeLists.txt
	tests/test_plan.cpp