* 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
if and switch are implicitly inline if the condition/target
expression is known at compile time.
instead of:
```
inline if (condition) ...
inline switch (target) ...
```
one can use:
```
if (comptime condition) ...
switch (comptime target) ...
```