* srml-contracts: Rename ext_scratch_copy to ext_scratch_read.
This is to disambiguate from the next ext_scratch_write function.
* Remove unnecessary OutputBuf and EmptyOutputBuf.
* Replace VmExecError with a result type of custom structs.
* Do not drop the scratch buffer on traps and regular returns.
This just reduces the number of allocations required during nested
contract calls and instantiations.
* Semantics for returning a status code and data from contract calls.
* Remove CallReceipt and InstantiateReceipt.
With forthcoming changes to return data from instantiate calls, the two
types of receipts become very similar to each other and to
ExecReturnValue. Instead, replace them with ExecReturnValue and
a regular 2-tuple in the case of instantiation.
* Modify contract function signatures to allow returning status codes.
* Introduce ext_sandbox_write runtime function.
* Test all the things.
* Bump node runtime spec version.
* Style fixes.
* srml-contracts: Remove hard-coded code hashes from tests.
This makes it easier to update existing and add new test Wasm modules.
* Test maximum contract storage write size.
* Implement storage value limit for contracts.
* Bump node runtime spec version.
* srml-contract: Move gas costs from Config to Schedule.
* srml-contract: Define Gas units fixed as u64.
This removes Gas as a configurable type on the contracts Trait.
* Bump node runtime spec/impl versions.
* Pass input data via the scratch buffer.
Remove calls to ext_input_*.
* Fix tests and docs
* Bump the version.
* Remove ext_input_* from COMPLEXITY.md
* Return back the length check and add more comments
* Update the documentation of the scratch buffer.
* Fix a silly mistake.
Jim Posen