builtin functions for division and remainder division

* add `@divTrunc` and `@divFloor` functions
 * add `@rem` and `@mod` functions
 * add compile error for `/` and `%` with signed integers
 * add `.bit_count` for float primitive types

closes #217
157af4332aAndrew Kelley committed on 5/7/2017, 3:13:12 AMparent866c841
21 files changedLine totals unavailable