move test files

examples/assign.rs

examples/assign2.rs

examples/assign_err.rs

examples/assign_err2.rs

examples/assign_err3.rs

examples/call.rs

examples/call2.rs

examples/call3.rs

examples/call_err.rs

examples/call_err2.rs

examples/call_mut_ref.rs

examples/call_ref.rs

examples/comment.rs

examples/deref_assign.rs

examples/deref_assign2.rs

examples/deref_assign3.rs

examples/if.rs

examples/let.rs

examples/let2.rs

examples/minimal.rs