* add `setFnTest`, `setFnVisible`, `setFnStaticEval`,
`setFnNoInline` builtin functions to replace previous
directive functionality
* add `coldcc` and `nakedcc` as keywords which can be used as part
of a function prototype.
* `setDebugSafety` builtin can be used to set debug safety features
at a per block scope level.
* closes#169
with byvalue return value or parameter.
currently we don't codegen byvalue parameters or return values
correctly for C compatibilty functions so instead of generating
incorrect code, we emit a compile error.
eventually we'll support this feature and remove the compile error.
See #180