1.2.5

This is a production release of go-codec.

This is a very important release, building upon the optimization introduced in v1.2.4.

Changes include:

• support gollvm in addition to gccgo in default high-performance mode
• support codec.safe and codec.notfastpath as preferred build tags (replacing safe and notfastpath)
• support Canonical mode with MissingFielder
• robust handling of codecgen caveats wrt Canonical|CheckCircularRef flags and MissingFielder implementations
• robust handling of transient values, where we track if a value has internal pointers and handle appropriately
• reduce use of global values: all in-use values are scoped to an Encoder or Decoder
• implement stateManager for Encoder/Decoder, supporting capture, reset and restore functions.
• side encoding or decoding can now reuse an Encoder/Decoder, leveraging state management to
  capture its state, do something else, then restore its state and continue
• support running all tests in parallel, so we can shake out any concurrency issues
• Fix issue in rpc where writer was not being flushed, causing a hang where reader was
  waiting on an encoded value
• Support shallow copies of a Handle, to support parallel execution where we need to
  temporarily change some Handler fields

This is the best release yet. Please try it out and share your experiences.