Logging utilities

[lkdvos]

This PR re-uses MPSKit functionality to handle the logging. I think it is a little cleaner, but I'm definitely open to suggestions.

[codecov]

Codecov Report

Attention: Patch coverage is 97.87234% with 1 line in your changes missing coverage. Please review.

Files	Coverage Δ
src/PEPSKit.jl	100.00% <ø> (ø)
src/algorithms/peps_opt.jl	95.83% <ø> (ø)
src/algorithms/ctmrg.jl	94.66% <97.87%> (-0.16%)	⬇️

[leburgel]

Looks good to me, but we should probably increase the verbosity in the examples and tests to at least verbosity=2, since level 1 got less verbose by default. None of the tests actually output log anything CTMRG-related here as far as I can tell. Also, it would be good to document what the different verbosity levels actually do (probably in the CTMRG docstring, which is now out of date with the possible levels).

[pbrehmer]

I agree, that probably the default verbosity should be changed and that a quick explanation of levels 0 to 3 would be useful to have in the CTMRG docstring. Other than that, I find the new logging machinery really neat (and also makes it more elegant to log on a HPC environment). Thanks!

[pbrehmer]

Except for the verbosity in PEPSOptimize I find this really nice and useful. Thanks!