Create DDEX parser in Rust

[denciu]

Links to #57

Rust provides some tools to parse XML but first entire schema needs to be translated to Rust structs. Tools used to achieve this:

• yaserde - tool used to (de)serialize XML
• xml-schema - tool used to generate Rust structs out of XSD files that are compatible with yaserde

Structs generated with xml-schema are far from being complete so I need to do some manual work here:

• remote linked schemas are not included in type generation, xsd files need to be merged and naming collisions need to be resolved
• xsd needs is way too heavy to work on it, it needs to be slimmed by removing annotations
• some xs:complexTypes that are extended are generated incorrectly
• optional sequence is omitted (DisplayCredits)
• recursive ResourceGroup is not parsed
• empty implementations for types like Period, PeriodWithStartDate, PeriodWithoutFlags
• implement xs:pattern - validation with regex
• implement xs:enumeration - validation with set of items
• implement xs:choice

Some validations/fields parsing that are irrelevant for our purposes (but essential in proving xml validity) may be skipped for PoC.