oas3: v0.6.0

• Add from_str() function.
• Add spec::SecurityScheme::MutualTls enum variant.
• Add spec::SecurityScheme::{ApiKey, Http, OAuth2, OpenIdConnect}::description fields.
• Add spec::SchemaTypeSet enum.
• Add spec::SchemaType::Null variant.
• The Spec::paths field is now optional to closer align with the spec.
• The spec::Operation::responses field is now optional to closer align with the spec.
• The spec::Schema::{exclusive_maximum, exclusive_minimum} fields are now of type Option<serde_json:Number> to closer align with the spec.
• Migrate YAML parsing to serde_yml. Exposed error type(s) have been altered.
• Add spec::Schema::nullable field.

oas3: v0.5.0

• Update http dependency to 1.