Add call infrastructure to ink_lang (#175)

* [core] add initial call builder implementation

* [core] add setters to CallBuilder

* [core] fix invalid mod import in no_std

* [lang] initial remote call implementation for ink_lang

* [examples] add ink-as-dependency crate feature to erc20 token contract

* [core] move calls and call error definitions

* [core] add ext_create support

* [*] apply rustfmt

* [core] expose ReturnType publicly

* [core] add ext_create impl on the SRML interfacing side

* [core] fix minor invalid module import

* [lang] split CallEnhancer into mut and immutable versions

* [lang] forward to call enhancers from short-version of remote calling

* [core] improve create builder to return the contract directly

* [lang] simplify env types code generation

* [lang] add create call builder code generation

* [lang] improve code gen by altering spans of the generated code

* [examples] add ink-as-dependency to all lang examples

* [cli] add ink-as-dependency to smart contract template

* [lang] fix code gen bug with forwarding references

* [lamg] move impls out of const item

It seems that inherent impls shouldn't be put inside a const item.

* [core] impl Default for Hash

* [lang] add Flush, scale::{Encode, Decode} for contracts as dependencies

* [examples] add example to call remote smart contracts

* [examples] remove invalid test code from delegator contract

* [abi] fix warning about suffixed tuple indices

* [lang] fix bug in generate-abi codegen for deploy handler with multiple args

* [lang] derive from type_metadata::Metadata for contract structs

* [examples] ran cargo fmt

* [examples] derive type_metadata::Metadata for Which

* [examples] make code hashes deploy inputs for delegator contract

* [core] rename gas_cost to gas_limit

* [core] remove parts that got re-introduced accidentally upon merge

* [examples] add a README to the delegator contract

* [examples] restructure delegator project structure

* [examples] fix Cargo.toml of delegator

* [lang] fix bug that ink-as-dependency derives Metadata for the state struct

* [lang] add getter for account_id of ink-as-dependency state structs

* [examples] adjust Delegator contract to make it work with old ABI generator

* [lang] import FromAccountId

* [examples] provide a build.sh script to deploy delegator contract

* [readme] add section about wabt and wasm-utils tools

* [readme] add off-chain test for the example smart contract

* [examples] add .value call to contract create calls of delegator

* [*] use fix-serialization branch of type-metadata

* [*] use type-metadata master branch again (PR was merged)

* [lang] update the noop compile test

* [lang] simplified the noop compile test doc comments

* [lang] fix compiletest for Flipper contract

* [lang] fix compile tests for incrementer contract

* [lang] fix compile tests for Events contract

* [scripts] do not check the Delegator for now (needs special treatment)

* [ci] update rust version from nightly-2019-08-13 to nightly-2019-08-30

* [examples] restructure delegator contract project structure

* [scripts] make check-examples script simpler again after delegator refactoring

* [examples] clean up Delegator contract

* [examples] improve build guidance of Delegator contract