Add capture data-type to representation.

The existing representation of lambda-capture was simply insufficient in
handling all the different cases that need to be handled.

NB. ~[this = this]~ is invalid syntax.
Migrate expressions to capture representation.
Migrate declarations to capture representation.
Migrate collections to capture representation.
Remove some stale debugging symbols.

I can't believe nobody spotted this already.
Migrate program to capture representation.
Fix ostringstream capture issues in prettify.

This was almost certainly a result of me migrating lambda captures.
Kill processRole call, pending better design of multi-instance engines.
Fix incorrectly namespaced terms in Literals.hpp.
Fix missing include in Context.hpp.
Fix swapped names in collection_patcher::patch invocation.
Tidy stringification of empty else-branches.
Move patching from context constructor to __patch.
Fix parenthesization of subscripts.
Move dispatch table population into context.
Fix usage of Binary "=" -> Assignment.
Fix broken createContexts.