first pass at zig build system

 * `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

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/langref.md b/doc/langref.md
index 7b6ba4b294..529191bf26 100644
--- a/doc/langref.md
+++ b/doc/langref.md
@@ -633,3 +633,10 @@ Invokes the panic handler function. By default the panic handler function
 calls the public `panic` function exposed in the root source file, or
 if there is not one specified, invokes the one provided in
 `std/special/panic.zig`.
+
+### @bitcast(comptime DestType: type, value: var) -> DestType
+
+Transmutes memory from one type to another without changing any bits.
+The source and destination types must have the same size. This function
+can be used to, for example, reinterpret a pointer, or convert a `f32` to a
+`u32`.