feat(xdg): add bin_dir, data_dirs, & config_dirs and add note about runtime_dir #119

Job	Run time
Outdated	0s
Formatting	14s
Test on macos-latest with Rust nightly	15s
Miri	34s
Test on macos-latest with Rust stable	17s
Test on macos-latest with Rust 1.54.0	2m 49s
Test on ubuntu-latest with Rust nightly	12s
Test on ubuntu-latest with Rust stable	7s
Test on ubuntu-latest with Rust 1.54.0	2m 32s
Test on windows-latest with Rust nightly	31s
Test on windows-latest with Rust stable	1m 15s
Test on windows-latest with Rust 1.54.0	2m 33s
	11m 19s

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