Release 0.4.0

Version 0.4.0 has improved support for samd21-based boards and has various compiler improvements.

It currently still requires Go 1.11, support for Go 1.12 will be added in a future release.

• compiler
  • switch to the hardfloat ABI on ARM, which is more widely used
  • avoid a dependency on objcopy (arm-none-eabi-objcopy etc.)
  • fix a bug in make([]T, n) where n is 64-bits on a 32-bit platform
  • adapt to a change in the AVR backend in LLVM 8
  • directly support the .uf2 firmware format as used on Adafruit boards
  • fix a bug when calling panic() at init time outside of the main package
  • implement nil checks, which results in a ~5% increase in code size
  • inline slice bounds checking, which results in a ~1% decrease in code size
• targets
  • samd21: fix a bug in port B pins
  • samd21: implement SPI peripheral
  • samd21: implement ADC peripheral
  • stm32: fix a bug in timekeeping
  • wasm: fix a bug in wasm_exec.js that caused corruption in linear memory when running on Node.js.