3rd pre-release version

Removed open_or_create mode.
Replaced std::cerr with the logger.
Bugfix in stl allocator regarding some member types such as propagate_on_container_copy_assignment.
Changed to store a UUID in a data store.
Brushed up documents, CMake file, and internal implementation.
Updated the CI configurations.
Bugfix in the benchmark, the utility, and the containers.

2nd pre-release version

Significant external and internal updates from v0.1.
Many public APIs are not backwards compatible.

Major updates are as follows:
Provides a space efficient snapshot that leverages reflink.
A lot of performance improvements, including employing thread- and CPU-level object caches.
Uses multiple backing files to store application data.
Application data segment (Metall heap) grows dynamically.
Automatically runs CI on Travis CI and LC GItLab CI.
Detailed document is available on Read the Docs.
Add some utilities for OpenMP and MPI environments.

Initial (pre) release

The first tag after all put on GitHub.