Add logging.

[jmjoy]

• Move Tracer reporting method to GrpcReporter.
• Add Logger and LogRecord api.
• Add logging integration tests.

[codecov-commenter]

Codecov Report

Merging #41 (7edfd1f) into master (c6ec104) will decrease coverage by 17.30%.
The diff coverage is 6.18%.

@@             Coverage Diff             @@
##           master      #41       +/-   ##
===========================================
- Coverage   44.70%   27.40%   -17.31%     
===========================================
  Files          14       17        +3     
  Lines         378      478      +100     
===========================================
- Hits          169      131       -38     
- Misses        209      347      +138     

Impacted Files	Coverage Δ
src/common/system_time.rs	0.00% <ø> (ø)
src/logging/logger.rs	0.00% <0.00%> (ø)
src/logging/record.rs	0.00% <0.00%> (ø)
src/reporter/grpc.rs	0.00% <0.00%> (ø)
src/reporter/mod.rs	0.00% <0.00%> (-100.00%)	⬇️
src/reporter/once_cell.rs	0.00% <0.00%> (ø)
src/skywalking_proto/v3/mod.rs	0.00% <ø> (ø)
src/trace/span.rs	0.00% <ø> (ø)
tests/trace_context.rs	0.00% <ø> (ø)
src/reporter/print.rs	46.66% <46.66%> (ø)
... and 3 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[jmjoy]

@wu-sheng It seems that skywalking-agent-test-tool does not support the mock of logging, it should be added to doing e2e for logging?

[wu-sheng]

Yes, it should be added.

[jmjoy]

skywalking-agent-test-tool
Add logging mock and validation.
apache/skywalking-agent-test-tool#39

[wu-sheng]

Please logging APIs in the readme doc.

[jmjoy]

Readme updated.