* In-progress os.ChildProcess.spawn implementation. See #204
* Add explicit cast from integer to error. Closes#294
* fix casting from error to integer
* fix compiler crash when initializing variable to undefined
with no type
* `zig build --export [obj|lib|exe]` changed to `zig build_obj`,
`zig build_lib` and `zig build_exe` respectively.
* `--name` parameter is optional when it can be inferred from the
root source filename. closes#207
* `zig build` now looks for `build.zig` which interacts with
`std.build.Builder` to describe the targets, and then the zig
build system prints TODO: build these targets. See #204
* add `@bitcast` which is mainly used for pointer reinterpret
casting and make explicit casting not do pointer reinterpretation.
Closes#290
* fix debug info for byval parameters
* sort command line help options
* `std.debug.panic` supports format string printing
* add `std.mem.IncrementingAllocator`
* fix const ptr to a variable with data changing at runtime.
closes#289
Andrew Kelley