v0.2.0

Feature release that expands COPY support, adds cancellation and profiling tools, and improves package-level documentation.

Highlights:

• add pg_cancel/1 and centralize row decoding around the active driver layers
• add binary COPY FROM STDIN with typed row input via binary(TypeSpecs, Rows)
• add streaming pg_copy_to/3 for COPY TO STDOUT with callback-delivered chunks
• add a row-decoding profiling harness and preserve the measured optimizations in the driver
• add package/module documentation plus a runnable examples/simple.pl example
• recover cleanly after COPY TO STDOUT callback failures and binary COPY server-side errors
• add byte-level COPY framing tests plus local PostgreSQL coverage for binary COPY and streaming COPY-out