[autoantohaki]

Before: every line of a log was printed, so finding the errors in a busy service meant piping through grep and losing level colors and stack traces along the way.

After: relay-logs -l warn app.log shows only warnings and worse, -g keeps lines matching a pattern, and -x drops lines matching one. They work with -f, so relay-logs -f -l error -x /health api.log follows only the errors that matter. Indented lines such as stack frames stay with the entry above them, so an error keeps its trace even though the frames have no level of their own.

Patterns are regular expressions and ignore case unless they contain an uppercase letter.

How: createFilter builds a predicate from the options and remembers, per source, whether the last entry was shown so continuation lines follow it. Invalid patterns and unknown level names are reported as usage errors with exit code 2.

This branch is stacked on #1; please merge that first.