inkwell

Fixes previous error on operands into

change into_* OperandValue variants into panicking

Adds AsValueRef impl to BasicBlock. This lets OperandValue implement AsValueRef to then genericize set_operand as anything Into<OperandValue> with extra From operators

Adds a few utility functions around debug information and changes instruction operand handling to support debug metadata, with some fixes to error messaging around value types too.

Fix comment typos in `test_conversion_to_pointer_value` (#605)