Kefir 0.4.0 release: * Implemented complex number support. * Implemented atomics support via software library (libatomic/libcompiler_rt). * Implemented DWARF-5 debug information generator. * Improved compatibility with GNU C language extensions (__auto and __typeof, imaginary numbers, inline assembly, visibility and linkage attributes, ranges in case labels and array initializers). * Implemented full 3-stage bootstrap to produce self-compiled portable package with Kefir, GNU As, GNU Ld and Musl libc. * Limited support for Yasm as a target assembler. * Optimizations in both generated code and compiler. * Bug fixes, improved correctness, formalization and extension of external program test suite.