Rustify core/src/core (#1122)

Small refactoring of one folder, if it makes sense I could extend the scope.
* Remove some cloning (real and just verbosity in the code)
* Naming conventions like to/into*
* Some Clippy's suggestions

I found that we don't use field init shorthand syntax, so I didn't touch this part, was it discussed before?

chain/src/chain.rs

@@ -30,8 +30,8 @@ use pipe;
 use store;
 use txhashset;
 use types::*;
-use util::secp::pedersen::{Commitment, RangeProof};
 use util::LOGGER;
+use util::secp::pedersen::{Commitment, RangeProof};
 
 /// Orphan pool size is limited by MAX_ORPHAN_SIZE
 pub const MAX_ORPHAN_SIZE: usize = 200;
@@ -260,7 +260,7 @@ impl Chain {
 		debug!(
 			LOGGER,
 			"Chain init: {} @ {} [{}]",
-			head.total_difficulty.into_num(),
+			head.total_difficulty.to_num(),
 			head.height,
 			head.last_block_h,
 		);

chain/src/pipe.rs

@@ -277,7 +277,7 @@ fn validate_header(header: &BlockHeader, ctx: &mut BlockContext) -> Result<(), E
 
 		let target_difficulty = header.total_difficulty.clone() - prev.total_difficulty.clone();
 
-		if header.pow.clone().to_difficulty() < target_difficulty {
+		if header.pow.to_difficulty() < target_difficulty {
 			return Err(Error::DifficultyTooLow);
 		}
 
@@ -297,8 +297,8 @@ fn validate_header(header: &BlockHeader, ctx: &mut BlockContext) -> Result<(), E
 			error!(
 				LOGGER,
 				"validate_header: BANNABLE OFFENCE: header cumulative difficulty {} != {}",
-				target_difficulty.into_num(),
-				prev.total_difficulty.into_num() + network_difficulty.into_num()
+				target_difficulty.to_num(),
+				prev.total_difficulty.to_num() + network_difficulty.to_num()
 			);
 			return Err(Error::WrongTotalDifficulty);
 		}

chain/src/txhashset.rs

@@ -930,7 +930,7 @@ impl<'a> Extension<'a> {
 			if pmmr::is_leaf(n) {
 				if let Some(out) = self.output_pmmr.get_data(n) {
 					if let Some(rp) = self.rproof_pmmr.get_data(n) {
-						out.to_output(rp).verify_proof()?;
+						out.into_output(rp).verify_proof()?;
 					} else {
 						// TODO - rangeproof not found
 						return Err(Error::OutputNotFound);