fix go lint (except comment on exported fields, error message with punct)

ast.go:70:1: comment on exported type MaybeRuleAST should be of the form "MaybeRuleAST ..." (with optional leading article)
eval.go:241:1: comment on exported method Evaluator.EvaluateVar should be of the form "EvaluateVar ..."
eval.go:14:2: don't use ALL_CAPS in Go names; use CamelCase
eval.go:15:2: don't use ALL_CAPS in Go names; use CamelCase
eval.go:16:2: don't use ALL_CAPS in Go names; use CamelCase
eval.go:431:2: don't use underscores in Go names; var makefile_list should be makefileList
main.go:29:2: var loadJson should be loadJSON
main.go:30:2: var saveJson should be saveJSON
ninja.go:19:2: struct field ruleId should be ruleID
para.go:15:9: if block ends with a return statement, so drop this else and outdent its block
para_test.go:21:2: don't use underscores in Go names; var num_tasks should be numTasks
parser.go:713:1: error should be the last type when returning multiple items
serialize.go:20:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:21:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:22:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:23:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:24:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:25:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:26:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:27:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:28:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:29:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:30:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:31:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:32:2: don't use ALL_CAPS in Go names; use CamelCase
serialize.go:230:6: func DumpDepGraphAsJson should be DumpDepGraphAsJSON
serialize.go:553:6: func LoadDepGraphFromJson should be LoadDepGraphFromJSON
serialize.go:437:9: if block ends with a return statement, so drop this else and outdent its block
var.go:174:1: receiver name should not be an underscore
var.go:175:1: receiver name should not be an underscore
var.go:176:1: receiver name should not be an underscore
var.go:177:1: receiver name should not be an underscore
var.go:178:1: receiver name should not be an underscore
var.go:180:1: receiver name should not be an underscore
var.go:183:1: receiver name should not be an underscore
var.go:187:1: receiver name should not be an underscore
var.go:191:1: receiver name should not be an underscore
diff --git a/para.go b/para.go
index c17c5c9..6ea178a 100644
--- a/para.go
+++ b/para.go
@@ -12,9 +12,8 @@
 func btoi(b bool) int {
 	if b {
 		return 1
-	} else {
-		return 0
 	}
+	return 0
 }
 
 func sendMsg(w io.Writer, data []byte) {