conform imports to schema defined in CONTRIBUTING.md (#150)

* use multi-import grouping

* terminate all newlines in import groups

* group go-fil-markets, as per style guide

* replace go-filecoin with go-fil-markets in CONTRIBUTING.md

Author: laser

pieceio/mocks/CarIO.go

@@ -4,19 +4,11 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-
 	"io"
 	"testing"
 
-	"github.com/filecoin-project/go-fil-markets/filestore"
-	fsmocks "github.com/filecoin-project/go-fil-markets/filestore/mocks"
-	"github.com/filecoin-project/go-fil-markets/pieceio"
-	"github.com/filecoin-project/go-fil-markets/pieceio/cario"
-	pmocks "github.com/filecoin-project/go-fil-markets/pieceio/mocks"
-
 	"github.com/filecoin-project/go-sectorbuilder"
 	"github.com/filecoin-project/specs-actors/actors/abi"
-
 	"github.com/ipfs/go-cid"
 	dag "github.com/ipfs/go-merkledag"
 	dstest "github.com/ipfs/go-merkledag/test"
@@ -25,6 +17,12 @@ import (
 	"github.com/ipld/go-ipld-prime/traversal/selector/builder"
 	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
+
+	"github.com/filecoin-project/go-fil-markets/filestore"
+	fsmocks "github.com/filecoin-project/go-fil-markets/filestore/mocks"
+	"github.com/filecoin-project/go-fil-markets/pieceio"
+	"github.com/filecoin-project/go-fil-markets/pieceio/cario"
+	pmocks "github.com/filecoin-project/go-fil-markets/pieceio/mocks"
 )
 
 func Test_ThereAndBackAgain(t *testing.T) {

pieceio/mocks/PieceIO.go

@@ -3,12 +3,12 @@ package pieceio
 import (
 	"io"
 
-	"github.com/filecoin-project/go-fil-markets/filestore"
 	"github.com/filecoin-project/specs-actors/actors/abi"
-
 	blocks "github.com/ipfs/go-block-format"
 	"github.com/ipfs/go-cid"
 	"github.com/ipld/go-ipld-prime"
+
+	"github.com/filecoin-project/go-fil-markets/filestore"
 )
 
 type WriteStore interface {