fixed some style issues, added tooling for docs

docs/core/rng.md

@@ -0,0 +1,16 @@
+# core/rng.h
+
+## class Rng — public interface
+
+### `: _eng(seed) { ... }`
+### `void seed(seed_type s) noexcept { ... }`
+### `_eng.seed(s);`
+### `double uniform01() { ... }`
+### `Int uniform_range(Int lo_inclusive, Int hi_exclusive) { ... }`
+### `Int uniform_range(Int hi_exclusive) { ... }`
+### `double uniform_range(double lo_inclusive, double hi_exclusive) { ... }`
+### `std::uint64_t poisson(double lambda) { ... }`
+### `T choose_weighted(const std::vector<std::pair<double, T>>& items) { ... }`
+### `return choose_weighted_impl(items.begin(), items.end());`
+### `T choose_weighted(std::initializer_list<std::pair<double, T>> items) { ... }`
+### `return choose_weighted_impl(items.begin(), items.end());`