Migrate existing tests to node-tap

[aqrln]

The consensus is we should use node-tap as the test framework instead of mocha and chai. This may be a gradual and incremental process.
We'll need to migrate:

• serde (#153)
• message parser (#168)
• errors (#167)
• connection (#183, #198, #199, #200)
• remote proxy (#198, #199)
• client (#183, #198)
• server (#183)