Documented missing FormType variables
Documented checked variable
Documented choice variables
Documented selectedchoice test
Added performance tip
Documented CollectionType variables
Documented Date(Time)Type variables
Extracted duplicated var tables
Documented date_pattern variable of DateType
Documented FileType variables
Documented MoneyType variables
Documented SubmitType variables
Documented TimeType variables
Added globals section
Added a note on caching
Documented custom engines and DelegatingEngine
Applied comments by @xabbuh
Made full stop usage consistent
Added a tip about hardcoding URLS in functional tests
Fixed a minor typo