For parsing and verification of of HTTP request and response bodies,
including optional checking the Content-Type field which the handler
previously didn't do.
Despite having common names between the request and response XML
structures the actual values which may appear in them are completely
disjoint. Splitting the types up makes the protocol easier to understand
when reading the code. When applicable, required fields like status are
passed to Add* methods.
- Avoid long argument lists and only pass values that are strictly
required such as status, fill in all other fields directly instead.
- Fill OS struct in requests based on local system.
- Define event and status codes as constants.
- Misc style tweaks.
