Add cross-compilation Makefile targets and tar-based releases.

Revamp the build system to be more inline with other Prometheus exporters.
Notably add Darwin and Windows build targets, and add support for releases
using tar files.

tools/vendor/mvdan.cc/lint/lint.go

@@ -0,0 +1,28 @@
+// Copyright (c) 2017, Daniel Martí <mvdan@mvdan.cc>
+// See LICENSE for licensing information
+
+// Package lint defines common interfaces for Go code checkers.
+package lint // import "mvdan.cc/lint"
+
+import (
+	"go/token"
+
+	"golang.org/x/tools/go/loader"
+	"golang.org/x/tools/go/ssa"
+)
+
+// A Checker points out issues in a program.
+type Checker interface {
+	Program(*loader.Program)
+	Check() ([]Issue, error)
+}
+
+type WithSSA interface {
+	ProgramSSA(*ssa.Program)
+}
+
+// Issue represents an issue somewhere in a source code file.
+type Issue interface {
+	Pos() token.Pos
+	Message() string
+}