Warnings with rustc 1.44.1

[gagath]

A set of warnings is appearing when compiling with this toolchain:

warning: trait objects without an explicit `dyn` are deprecated
  --> src/types.rs:94:32
   |
94 |     fn cause(&self) -> Option<&error::Error> {
   |                                ^^^^^^^^^^^^ help: use `dyn`: `dyn error::Error`
   |
   = note: `#[warn(bare_trait_objects)]` on by default

warning: `...` range patterns are deprecated
  --> src/utils.rs:26:13
   |
26 |         b'A'...b'F' => Ok(c - b'A' + 10),
   |             ^^^ help: use `..=` for an inclusive range
   |
   = note: `#[warn(ellipsis_inclusive_range_patterns)]` on by default

warning: `...` range patterns are deprecated
  --> src/utils.rs:27:13
   |
27 |         b'a'...b'f' => Ok(c - b'a' + 10),
   |             ^^^ help: use `..=` for an inclusive range

warning: `...` range patterns are deprecated
  --> src/utils.rs:28:13
   |
28 |         b'0'...b'9' => Ok(c - b'0'),
   |             ^^^ help: use `..=` for an inclusive range

warning: `...` range patterns are deprecated
  --> src/utils.rs:41:12
   |
41 |         0xa...0xf => val - 0xa + b'a',
   |            ^^^ help: use `..=` for an inclusive range

warning: `...` range patterns are deprecated
  --> src/utils.rs:42:12
   |
42 |         0x0...0x9 => val + b'0',
   |            ^^^ help: use `..=` for an inclusive range

warning: `...` range patterns are deprecated
  --> src/utils.rs:52:12
   |
52 |         0xA...0xF => val - 0xa + b'A',
   |            ^^^ help: use `..=` for an inclusive range

warning: `...` range patterns are deprecated
  --> src/utils.rs:53:12
   |
53 |         0x0...0x9 => val + b'0',
   |            ^^^ help: use `..=` for an inclusive range

warning: use of deprecated item 'std::error::Error::description': use the Display impl or to_string()
  --> src/types.rs:89:44
   |
89 |             Error::IoError(ref err) => err.description(),
   |                                            ^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: use of deprecated item 'std::error::Error::description': use the Display impl or to_string()
  --> src/types.rs:90:44
   |
90 |             Error::Parsing(ref err) => err.description(),
   |                                            ^^^^^^^^^^^

warning: 10 warnings emitted

A fix is proposed in #11.