Auto merge of #2282 - mcarton:clippy, r=alexcrichton

Auto merge of #2282 - mcarton:clippy, r=alexcrichton

For information, here is the [log before and after](https://gist.github.com/mcarton/684c030321c4c60d6bc9) with Clippy.
Remaining warnings from Clippy are mostly false positive or `str` to `string` conversion (too many of them for this PR).

```
warnings before:
     cmp_owned : 2
     cyclomatic_complexity : 1
     deprecated : 11
     explicit_iter_loop : 57
     identity_op : 3
     len_without_is_empty : 3
     len_zero : 20
     let_and_return : 3
     map_clone : 14
     needless_lifetimes : 4
     needless_return : 24
     ok_expect : 2
     option_map_unwrap_or : 10
     private_in_public : 28
     redundant_closure : 2
     should_implement_trait : 2
     single_match : 3
     str_to_string : 112
     string_to_string : 12
     type_complexity : 3
     unnecessary_mut_passed : 2
     unneeded_field_pattern : 3
     unused_lifetimes : 1
     unused_variables : 2
     while_let_loop : 2

warnings after:
     cmp_owned : 2
     cyclomatic_complexity : 1
     identity_op : 1
     let_and_return : 3
     map_clone : 1
     needless_return : 3
     ok_expect : 2
     option_map_unwrap_or : 1
     private_in_public : 28
     should_implement_trait : 2
     str_to_string : 80
     type_complexity : 3
     while_let_loop : 2
```