closes#291
This changes the error message "return value ignored" to "expression value is ignored".
This is because this error also applies to {1;}, which has no function calls.
Also fix ignored expression values in std and test.
This caught a bug in debug.readAllocBytes where an early Eof error would have been missed.
See #219.
* Fix assertion failure when switching on type.
Closes#310
* Update zig build system to support user defined options.
See #204
* fmt.format supports {sNNN} to set padding for a buffer arg.
* add std.fmt.bufPrint and std.fmt.allocPrint
* std.hash_map.HashMap.put returns the previous value
* add std.mem.startsWith