Cargo build results in a number of warnings

[cswindle]

There are currently quite a few warnings produced when building this crate:

   Compiling aws-sdk-rust v0.1.42 (file:///home/cns/git/aws-sdk-rust)
warning: use of deprecated item 'std::ascii::AsciiExt': use inherent methods instead
  --> src/aws/common/credentials.rs:27:5
   |
27 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(deprecated)] on by default

warning: use of deprecated item 'std::ascii::AsciiExt': use inherent methods instead
  --> src/aws/common/signature.rs:30:5
   |
30 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^

warning: use of deprecated item 'std::ascii::AsciiExt': use inherent methods instead
  --> src/aws/s3/s3client.rs:18:5
   |
18 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^

warning: use of deprecated item 'openssl::sign::Signer::finish': renamed to sign_to_vec
   --> src/aws/common/signature.rs:354:18
    |
354 |             hmac.finish().unwrap().to_base64(STANDARD)
    |                  ^^^^^^

warning: use of deprecated item 'openssl::sign::Signer::finish': renamed to sign_to_vec
   --> src/aws/common/signature.rs:474:10
    |
474 |     hmac.finish().unwrap().to_hex().to_string()
    |          ^^^^^^

warning: use of deprecated item 'openssl::sign::Signer::finish': renamed to sign_to_vec
   --> src/aws/common/signature.rs:481:23
    |
481 |     let k_date = hmac.finish().unwrap();
    |                       ^^^^^^

warning: use of deprecated item 'openssl::sign::Signer::finish': renamed to sign_to_vec
   --> src/aws/common/signature.rs:486:25
    |
486 |     let k_region = hmac.finish().unwrap();
    |                         ^^^^^^

warning: use of deprecated item 'openssl::sign::Signer::finish': renamed to sign_to_vec
   --> src/aws/common/signature.rs:491:26
    |
491 |     let k_service = hmac.finish().unwrap();
    |                          ^^^^^^

warning: use of deprecated item 'openssl::sign::Signer::finish': renamed to sign_to_vec
   --> src/aws/common/signature.rs:496:10
    |
496 |     hmac.finish().unwrap()
    |          ^^^^^^

warning: unused import: `std::ascii::AsciiExt`
  --> src/aws/common/credentials.rs:27:5
   |
27 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(unused_imports)] on by default

warning: unused import: `std::ascii::AsciiExt`
  --> src/aws/common/signature.rs:30:5
   |
30 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^

warning: unused import: `std::ascii::AsciiExt`
  --> src/aws/s3/s3client.rs:18:5
   |
18 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^