Major rework of codebase

- Get rid of 'core' and move CLI to cmd/gas directory
- Migrate (most) tests to use Ginkgo and testutils framework
- GAS now expects package to reside in $GOPATH
- GAS now can resolve dependencies for better type checking (if package
  on GOPATH)
- Simplified public API

testutils/source.go

@@ -0,0 +1,193 @@
+package testutils
+
+// CodeSample encapsulates a snippet of source code that compiles, and how many errors should be detected
+type CodeSample struct {
+	Code   string
+	Errors int
+}
+
+var (
+	// SampleCodeG101 code snippets for hardcoded credentials
+	SampleCodeG101 = []CodeSample{{`
+package main
+import "fmt"
+func main() {
+	username := "admin"
+	password := "f62e5bcda4fae4f82370da0c6f20697b8f8447ef"
+	fmt.Println("Doing something with: ", username, password)
+}`, 1}, {`
+// Entropy check should not report this error by default
+package main
+import "fmt"
+func main() {
+	username := "admin"
+	password := "secret"
+	fmt.Println("Doing something with: ", username, password)
+}`, 0}, {`
+package main
+import "fmt"
+var password = "f62e5bcda4fae4f82370da0c6f20697b8f8447ef"
+func main() {
+	username := "admin"
+	fmt.Println("Doing something with: ", username, password)
+}`, 1}, {`
+package main
+import "fmt"
+const password = "f62e5bcda4fae4f82370da0c6f20697b8f8447ef"
+func main() {
+	username := "admin"
+	fmt.Println("Doing something with: ", username, password)
+}`, 1}, {`
+package main
+import "fmt"
+const (
+	username = "user"
+	password = "f62e5bcda4fae4f82370da0c6f20697b8f8447ef"
+)
+func main() {
+	fmt.Println("Doing something with: ", username, password)
+}`, 1}, {`
+package main
+var password string
+func init() {
+	password = "f62e5bcda4fae4f82370da0c6f20697b8f8447ef"
+}`, 1}, {`
+package main
+const (
+	ATNStateSomethingElse = 1
+	ATNStateTokenStart = 42
+)
+func main() {
+	println(ATNStateTokenStart)
+}`, 0}, {`
+package main
+const (
+	ATNStateTokenStart = "f62e5bcda4fae4f82370da0c6f20697b8f8447ef"
+)
+func main() {
+	println(ATNStateTokenStart)
+}`, 1}}
+
+	// SampleCodeG102 code snippets for network binding
+	SampleCodeG102 = []CodeSample{
+		// Bind to all networks explicitly
+		{`
+package main
+import (
+	"log"
+   	"net"
+)
+func main() {
+	l, err := net.Listen("tcp", "0.0.0.0:2000")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer l.Close()
+}`, 1},
+
+		// Bind to all networks implicitly (default if host omitted)
+		{`
+package main
+import (
+	"log"
+   	"net"
+)
+func main() {
+   	l, err := net.Listen("tcp", ":2000")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer l.Close()
+}`, 1},
+	}
+	// SampleCodeG103 find instances of unsafe blocks for auditing purposes
+	SampleCodeG103 = []CodeSample{
+		{`
+package main
+import (
+	"fmt"
+	"unsafe"
+)
+type Fake struct{}
+func (Fake) Good() {}
+func main() {
+	unsafeM := Fake{}
+   	unsafeM.Good()
+   	intArray := [...]int{1, 2}
+   	fmt.Printf("\nintArray: %v\n", intArray)
+   	intPtr := &intArray[0]
+   	fmt.Printf("\nintPtr=%p, *intPtr=%d.\n", intPtr, *intPtr)
+   	addressHolder := uintptr(unsafe.Pointer(intPtr)) + unsafe.Sizeof(intArray[0])
+   	intPtr = (*int)(unsafe.Pointer(addressHolder))
+   	fmt.Printf("\nintPtr=%p, *intPtr=%d.\n\n", intPtr, *intPtr)
+}`, 3}}
+
+	// SampleCodeG104 finds errors that aren't being handled
+	SampleCodeG104 = []CodeSample{
+		{`
+package main
+import "fmt"
+func test() (int,error) {
+	return 0, nil
+}
+func main() {
+	v, _ := test()
+	fmt.Println(v)
+}`, 1}, {`
+package main
+import (
+	"io/ioutil"
+	"os"
+	"fmt"
+)
+func a() error {
+	return fmt.Errorf("This is an error")
+}
+func b() {
+	fmt.Println("b")
+	ioutil.WriteFile("foo.txt", []byte("bar"), os.ModeExclusive)
+}
+func c() string {
+	return fmt.Sprintf("This isn't anything")
+}
+func main() {
+	_ = a()
+	a()
+	b()
+	c()
+}`, 3}, {`
+package main
+import "fmt"
+func test() error {
+	return nil
+}
+func main() {
+	e := test()
+	fmt.Println(e)
+}`, 0}}
+
+	// SampleCodeG401 - Use of weak crypto MD5
+	SampleCodeG401 = []CodeSample{
+		{`
+package main
+import (
+	"crypto/md5"
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+func main() {
+	f, err := os.Open("file.txt")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer f.Close()
+
+	h := md5.New()
+	if _, err := io.Copy(h, f); err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%x", h.Sum(nil))
+}`, 1}}
+)