Change dependencies

[mathisloge]

Is your feature request related to a problem? Please describe.

I think it might make sense to switch to some other dependencies, which might be more maintained. I don't want to be rude here or something else, but snapcast depends on aixlog and popl which haven't seen any commits since 3 years now.

I would take the work on me to change the deps as follows:

• Introduce https://github.com/fmtlib/fmt for all string formatting. to_string especially for floats and double it is quite slow and inaccurate.
• aixlog -> spdlog (only dependency is fmt) (especially good to have the different log sinks, systemd-journal, android, etc.)
• popl -> CLI11 (can parse ini and toml config files, so the config format won't have to change)

Those are all really common and high quality libraries and available on the typical systems:

• fmt https://packages.ubuntu.com/search?keywords=libfmt-dev
• spdlog https://packages.ubuntu.com/search?keywords=spdlog
• cli11 https://packages.ubuntu.com/search?keywords=libcli11 (could also be used as a single header file)

I hope to get more familar with the source code with this work to contribute more in the future, since it works really great already for me at home.