feat: replace custom log with env_logger

[brianmcgee]

For the most part this is a like for like replacement which adds colorized output but with two minor deviations from master.

Log format

The log output does not include a : after the log level:

# before
[DEBUG]: load config: 1.68ms (Δ 1.68ms)
[DEBUG]: Found elm-format at /nix/store/ph20y12g5bi2d3xqfyv939v295w9w45s-elm-format-0.8.5/bin/elm-format
[DEBUG]: built glob set; 0 literals, 0 basenames, 0 extensions, 0 prefixes, 0 suffixes, 1 required extensions, 0 regexes
[DEBUG]: Found gofmt at /nix/store/81hx17lnmjafllfl1125g4n8qgwp5j9w-go-1.18.5/bin/gofmt

# after
[DEBUG] load config: 1.72ms (Δ 1.72ms)
[DEBUG] Found elm-format at /nix/store/ph20y12g5bi2d3xqfyv939v295w9w45s-elm-format-0.8.5/bin/elm-format
[DEBUG] built glob set; 0 literals, 0 basenames, 0 extensions, 0 prefixes, 0 suffixes, 1 required extensions, 0 regexes
[DEBUG] Found gofmt at /nix/store/81hx17lnmjafllfl1125g4n8qgwp5j9w-go-1.18.5/bin/gofmt

Verbosity flag

The version in master does not respect the number of times a -v flag is set: -v, -vv, and -vvv etc all result in the same log level: TRACE.

This version does respect the -v flag:

https://github.com/brianmcgee/treefmt/blob/a4aca2f1ce8b71d500d13e86d149e613e4c3feb2/src/main.rs#L17-L26

Closes #163, closes #196

[zimbatm]

sounds good!