* Get rid of Stack error
* Add UnexpectedSignature error and remove Value err
* Publish FuncInstance::invoke
* Rename Trap to TrapKind
* Replace Trap with struct. Enum is now TrapKind
* Fixes
* Update value.rs
* Avoid reversing parameter types iter.
* Add impl From<TrapKind> for Trap
* Remove redundant clone in prepare_function_args.
* Use .into() to convert TrapKind into Trap
* Introduce Trap struct.
* get_local can't fail.
* Add MemoryOutOfBounds trap.
* from_little_endian use slice instead of vec.
* MemoryAccessOutOfBounds for mem get and set.
* from_little_endian conversion can't fail.
* call_indirect traps.
* DivisionByZero and InvalidConversionToInt
* Use traps in value to convey an error
* select: int condition on stack top
* if: int condition on stack top
* Assert pops.
* Another protions of assert pops
* Introduce ValueStack
Also, hide FunctionContext and remove some stale code
* Traps in execution
* Make it compile.
* Check args before invoke.
* Document RuntimeArgs.
* Update host.rs
* Add rustdoc for Trap.
Sergey Pepyakin