Add an RPC method for calling a contract. (#3563)

* Sketch

* Some work on docs.

* Doc improvements.

* More docs.

* Some more docs.

* Yet another comment.

* Bump impl_version.

* Accept the block hash

* Use NumberOrHex

* Update node/rpc/src/contracts.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Move rpc/primitives

substrate/srml/contracts/src/exec.rs

@@ -75,11 +75,12 @@ pub type ExecResult = Result<ExecReturnValue, ExecError>;
 /// wrap the error string into an ExecutionError with the provided buffer and return from the
 /// enclosing function. This macro is used instead of .map_err(..)? in order to avoid taking
 /// ownership of buffer unless there is an error.
+#[macro_export]
 macro_rules! try_or_exec_error {
 	($e:expr, $buffer:expr) => {
 		match $e {
 			Ok(val) => val,
-			Err(reason) => return Err(ExecError { reason, buffer: $buffer }),
+			Err(reason) => return Err($crate::exec::ExecError { reason, buffer: $buffer }),
 		}
 	}
 }
@@ -191,15 +192,6 @@ pub trait Loader<T: Trait> {
 	fn load_main(&self, code_hash: &CodeHash<T>) -> Result<Self::Executable, &'static str>;
 }
 
-/// Struct that records a request to deposit an event with a list of topics.
-#[cfg_attr(any(feature = "std", test), derive(Debug, PartialEq, Eq))]
-pub struct IndexedEvent<T: Trait> {
-	/// A list of topics this event will be deposited with.
-	pub topics: Vec<T::Hash>,
-	/// The event to deposit.
-	pub event: Event<T>,
-}
-
 /// A trait that represent a virtual machine.
 ///
 /// You can view a virtual machine as something that takes code, an input data buffer,