feat: more logs & configurable log level

[jkowalleck]

Changed

• Log output is less verbose, can be re-enabled via CLI switch --verbose
  Warnings and errors are still displayed as before.
  This is considered a non-breaking change, since only informational logs and debug information is affected.

Added

• CLI switch -v, --verbose to increase output verbosity
  May be used multiple times, like -vvv.
• More logs on info-level
• More logs on debug-level

fixes #158

[jkowalleck]

debatable, whether this is a breaking change or not.
i'd argue that it is not, since the console log output was never API-like, and was intended for humans.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.15%	✅ 91.30% (target: 80.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (0d684b9)	1092	936	85.71%
Head commit (a918ec2)	1146 (+54)	984 (+48)	85.86% (+0.15%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1131)	23	21	91.30%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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