Enforce lint checks

[rossmuir]

Add the following lint checks to lib.rs (crust is a good example to check)

#![deny(deprecated, improper_ctypes, missing_docs, non_shorthand_field_patterns,
overflowing_literals, plugin_as_library, private_no_mangle_fns, private_no_mangle_statics,
raw_pointer_derive, stable_features, unconditional_recursion, unknown_lints, unsafe_code,
unsigned_negation, unused, unused_allocation, unused_attributes, unused_comparisons,
unused_features, unused_parens, while_true)] 

#![warn(trivial_casts, trivial_numeric_casts, unused_extern_crates, unused_import_braces,
unused_qualifications, variant_size_differences)]

[Fraser999]

Addressed in #63.