*: generate the code for type check as a preprocess (#59)

Add a preprocess to handle type check.
In the preprocess, sexp start with .type and .declare keeps unchange.
The other expressions change to (infer.check-type exp ...)

runtime: pack stack / pc / frees fields etc together into one struct (#…

…52)

lib/toc: support load builtin function

it works by compile cora to c; compile c to so; load so