* `Map`: fixed `discard`

* small extension to GLM test
* vector accessors use new repr format

* added default copy constructor to Value

* support for calling argument lists
* pointers don't move their arguments on attribute access

* Set: a custom hash function can now be specified

* further fixes for double drops

* fixed accidental double drops when returning from nested expressions

* reverted last commit

* fixed accidental double dropping of values; expression blocks whose result was noreturn still attempted to clean up the scope, which had already been cleaned up

* Array: additional annotation

* Array: changed destructor from an inline to a fn

* removed `has no default initializer` error messages from aggregate constructors to let the original errors through
* added `plain?` compile time function to check if a value or type is plain

* String: allow explicit conversion of native string type to `String`

* default array constructor now recursively constructs elements and allows passing initializing arguments

* String: support for casting to `string`

* added `raiseof` in addition to `returnof` to allow querying exception type

* core: added tau constant

* Rc: added double free debugging support
* fixed ubsan/asan build option
* disabled extended debug info generation for now, as it can trigger a double free in the LLVM codebase
* small adjustments for building with LLVM 11 (not complete yet)

* prover: `inttoptr` correctly propagates view state or instantiates unique type
* `Rc`: metadata now lives in the same allocation as the payload, so that each `Rc` object is now of pointer size

* `enum`: added support for `tostring`
* `enum`: using `repr` or `tostring` on an enum constant will yield a constant string