use spdlog instead of std::cout

[papadpickle]

• use spdlog instead of std::cout
• use clang-tidy for code formatting, by-default google style used

[papadpickle]

This commit is just to present the style and look of logging done via spdlog as well as code formatting done via clang-tidy. Both are discretionary but can make life easier going forward.

spdlog is a pretty good logger, supporting the fmt as well as other options like file logging in case required in future. https://github.com/gabime/spdlog

i have just added to account subscribe example for the moment. in case the pr is accepted, we can proceed with other files. this is how the logging may look.

[mschneider]

1. spdlog looks great
2. clang-tidy is a hassle to install on mac, recommend to go with clang-format as a start (which is widely available). Happy to switch to google code style. Please include a .clang-format config file and add a ci-check that enforces the code style on github actions.

Probably best to do both in separate PRs, so we can continue merging more work in between.

[papadpickle]

cool, ill split the stuff and raise seperate PRs.