Import type_erasure
Initial handling for associated types.
Initial implementation of same_type.  Start rewriting iterators to use deduced.
Update example to use the new iterator concept.
Doc updates.
There's no good reason for placeholder to use CRTP.  Remove it.
Fix bug in example.
Switch the key and value.
Finish iterator rewrite.
Handle duplicate uses of same_type.
Handle same_type in conversions.
Add tests for binding and fix some bugs that this exposed.
Avoid silently passing through unbound placeholders.  This fixes an accepts invalid error demonstrated by the test case.
Handle assignment of any references.
Variadic template implementation of tuple.
Some doc fixes.
Make sure that include scanner finds construct.hpp.
Some doc cleanup.
Try to document concepts precisely and add some discussion about how the interface evolved.
Doc tweaks.