Version 4 update

[SamJaarsma]

Several improvements from reviews:

• Split the travellers message into a basic message used for search and an extended message for confirming the booking
• Add a disclaimer for licensed code-types like GiataID and DRV GlobalTypes
• Better explain the "unspecified" use in enums
• Activity message: reorganized/cleaned-up to use just 3 levels: product_code, unit_code and service_code. Added proper explanation
• Added on-request/available status in search results
• Transport message: removed trip departure and arrival as it can be derrived from the first and last segment to avoid contradictions
• Explained sequence number logic for transport message
• All ProductList messages: made product_status and enum
• Added missing last modified timestamp to ActivityProductList and ActivityProductInfo
• Improved version explanation
• Transport message move servicefact to TripSegment
• Transport message include change policies
• Improve explanation for SearchResponseMetadata metadata, context
• Review multi room explanation
• Review currency message to allow for crypto, create string and specify number of decimals in an int32 (between 2 and 18)

[havan]

I will update the code and push to this PR the changes that are simple fixes, typos etc to save time.

[havan]

I've added multiple comments though out the changes.

[havan]

specify number of decimals in an int32 (between 2 and 18)

Why between 2 and 18? It can be any positive number and also it can be zero. Am I missing something?
(Well, it can be negative numbers also, math works but it's confusing)

[SamJaarsma]

specify number of decimals in an int32 (between 2 and 18)

Why between 2 and 18? It can be any positive number and also it can be zero. Am I missing something? (Well, it can be negative numbers also, math works but it's confusing)

changed to 0-18

[havan]

LGTM