Performance improvements

[alexfernandez]

Performance has increased from 17 krps to 20 krps. Command:

$ node bin/loadtest.js -n 1000000 -c 100 http://localhost:80/ --cores 3

Measurements on a 6-core Intel i5-12400T processor against a local nginx server, only three cores running loadtest.

Performance improvements:

• Use crypto.randomUUID() to generate ids, also avoids duplicates.
• Store requests in a map instead of an object.
• Add microprofiler as a dev dependency for ease of use.
• Use buffer concatenation instead of string concatenation.
• Avoid populating result object if there are no contentInspector or statusCallback.

Also in this PR:

• Remove versioning from readme, add to compatibility.
• Simplify callbacks and remove second-order functions.
• Many renames for clarity.

For immediate release as v7.1.0.