Made benchmarks runnable

[WaDelma]

I tried to run benchmarks and noticed that they don't work:

• bitsets were moved to different place, were private and didn't have documentations
• There were mutability problems with bunch of benchmarks.

After fixing these, benchmarks work, but create_now test panics:

test world::create_now              ... thread 'main' panicked at 'index out of bounds: the len is 1024 but the index is 1024', src\libcollections\vec.rs:1401
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: specs::world::Allocator::allocate
   1: <specs::world::World<C>>::create_now
   2: benches::world::create_now
   3: test::run_test
   4: test::run_tests
   5: test::run_tests_console
   6: test::test_main
   7: test::test_main_static
   8: benches::__test::main
   9: std::panicking::try::do_call
  10: __rust_maybe_catch_panic
  11: std::rt::lang_start
  12: main
  13: __tmainCRTStartup
  14: unit_addrs_search
  15: unit_addrs_search

[kvark]

Thank you! We've got to figure out why it panics.