clean up build
Moved `float-complex?' and `number->float-complex' to `math/base',
documented them
Documented `flexpt1p'
Removed `samples->immutable-hash' (not covariant anyway; not going to
use hashes)
original commit: 6f1ffecc2374f2874c1942fe0558420b74cbe223
Made return types of `flvector-length' and `unsafe-flvector-length' more precise (they return Index)
original commit: ac424a73a5f3fa81d34f11585ff80b63b5cdebb6
