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

import_tracker_test.go

@@ -0,0 +1,30 @@
+package gas_test
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("ImportTracker", func() {
+	var (
+		source string
+	)
+
+	BeforeEach(func() {
+		source = `// TODO(gm)`
+	})
+	Context("when I have a valid go package", func() {
+		It("should record all import specs", func() {
+			Expect(1).Should(Equal(1))
+			Fail("Not implemented")
+		})
+
+		It("should correctly track aliased package imports", func() {
+			Fail("Not implemented")
+		})
+
+		It("should correctly track init only packages", func() {
+			Fail("Not implemented")
+		})
+	})
+})