Add SPDX support (#445)

* add initial spdx support

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* expose FileOwner and use in SPDX presenter

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add initial json support for SPDX

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add remaining package fields

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add spdx license list generation + tests

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* keep fileOwner unexported from pkg

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* restore cli test util

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add external refs to spdx tag-value format

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add golang support to CPE generation

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* use tag-value format as default "spdx" format flavor

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add tests around spdx presenters + refactor presenter tests

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add bouncer exception for spdx tools-golang repo

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* remove spdx model questions

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/spdxlicense/license_list_test.go

@@ -0,0 +1,14 @@
+package spdxlicense
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLicenceListIDs(t *testing.T) {
+	// do a sanity check on the generated data
+	assert.Equal(t, "0BSD", licenseIDs["0bsd"])
+	assert.Equal(t, "ZPL-2.1", licenseIDs["zpl-2.1"])
+	assert.NotEmpty(t, Version)
+}