fix(HashMap): remove warnings
fix(enums): Add pub use/namespacing where required

BREAKING CHANGE: This change will require downstream users to reference
mime types using their namespace. i.e. MediaType::Json

I added pub use in places where the enums wouldn't be poluting user
namespaces with a large amount of names.
chore(dependencies): add dependency on cargoified libtime
chore(hashmap): update depreciated code to use get
Merge branch 'master' of https://github.com/nickel-org/nickel.rs