v0.15.0

Many thanks to @demarchenac, @Demivan, @david-plugge, @abd2561024 and @ooga for contributing to this release.

• Add possibility to define path of pipeline issue (issue #133)
• Add support for enums as key of record and recordAsync schema (issue #134)
• Add support for default values to optional, optionalAsync, nullable, nullableAsync, nullish and nullishAsync schema (issue #96, #118)
• Add getDefault method to get default value of schema (issue #105)
• Deprecate withDefault method in favor of optional schema