Treat IncDecStmt as AssignStmt

`++` and `--` operator are very similar to `x = x + 1` so we make it
simple and just treat it as an assignment.

Closes #120

testdata/src/default_config/generic_handling.go

@@ -557,3 +557,19 @@ func OnlyCheckTwoLinesAboveIfAssignment() {
 		return result, err
 	}
 }
+
+func IncrementDecrement() {
+	a := 1
+	a++
+	a--
+	b := 2
+
+	if true {
+		b--
+	}
+	b++ // want "assignments should only be cuddled with other assignments"
+
+	go func() {}()
+	b++            // want "assignments should only be cuddled with other assignments"
+	go func() {}() // want "only one cuddle assignment allowed before go statement"
+}

testdata/src/default_config/generic_handling.go.golden

@@ -597,3 +597,22 @@ func OnlyCheckTwoLinesAboveIfAssignment() {
 		return result, err
 	}
 }
+
+func IncrementDecrement() {
+	a := 1
+	a++
+	a--
+	b := 2
+
+	if true {
+		b--
+	}
+
+	b++ // want "assignments should only be cuddled with other assignments"
+
+	go func() {}()
+
+	b++ // want "assignments should only be cuddled with other assignments"
+
+	go func() {}() // want "only one cuddle assignment allowed before go statement"
+}

wsl.go

@@ -508,7 +508,8 @@ func (p *processor) parseBlockStatements(statements []ast.Stmt) {
 				continue
 			}
 
-			if _, ok := previousStatement.(*ast.AssignStmt); ok {
+			switch previousStatement.(type) {
+			case *ast.AssignStmt, *ast.IncDecStmt:
 				continue
 			}
 
@@ -533,6 +534,14 @@ func (p *processor) parseBlockStatements(statements []ast.Stmt) {
 			}
 
 			p.addWhitespaceBeforeError(t, reasonAssignsCuddleAssign)
+		case *ast.IncDecStmt:
+			switch previousStatement.(type) {
+			case *ast.AssignStmt, *ast.IncDecStmt:
+				continue
+			}
+
+			p.addWhitespaceBeforeError(t, reasonAssignsCuddleAssign)
+
 		case *ast.DeclStmt:
 			if !p.config.AllowCuddleDeclaration {
 				p.addWhitespaceBeforeError(t, reasonNeverCuddleDeclare)