-Added CI yaml file for workflows
-Added `doctest` as dependency
-Added test target executable to CMakeLists.txt
-Renamed `bin` scripts to remove `gdpm*` prefix
-Updated `SQLite 3` dependency in CMakeLists.txt
-Implement basic unit testing in `tests/basic.cpp`
-Fixed issue with handling `fmt` strings
-Fixed issue where `gdpm` would to work because of missing directory
-Changed `constexpr const char *` constants to use `const std::string`
string instead to use with `HOME` variable
-Changed where packages are stored. Now, they should stored in the
user's `$HOME/.config/gdpm/packages.db` by default. This may change to
use `$HOME/.cache/gdpm/packages.db` by default in the future.
