Implementation of ink! env (revision 3) (#312)
* [core] initial implementation of env revision 3 * add engine abstraction layer and implement api functions * add support for dispatch_call to env3 * add missing invoke_runtime to api.rs * [core] fix restore_contract docs * [core] initial implementation of off-chain environment * [core] clean-up of env3 fundamental types * [core] add WasmEnv::reset_buffer * show test submodule of env3 when compiling with rustdoc * [core] initial implementation of the off-chain env instance Also many other adjustments. * [core] further enhancements to off-chain env * [core] implement untyped Env for off-chain environment * [core] implemented a good chunk of TypedEnv for the off-chain environment * [core] minor improvements to env3 * [core] further improvements and additions to test-api of env3 * [core] remove former test-api file * [core] env3: add support for ext_tombstone_deposit * [core] env3: add setting of rent allowa...