Add goreleaser config to help automate builds for various platforms

We're currently building the following targets:
- Linux 386/x64/armv6/arm64
- Windows 386/x64
- macOS x64

.goreleaser.yml

@@ -0,0 +1,47 @@
+env:
+  - GO111MODULE=on
+before:
+  hooks:
+  - go mod download
+builds:
+  -
+    binary: gold
+    ldflags: -s -w -X main.Version={{ .Version }} -X main.CommitSHA={{ .Commit }}
+    goos:
+      - linux
+      - darwin
+      - windows
+    goarch:
+      - amd64
+      - arm64
+      - 386
+      - arm
+    goarm:
+      - 6
+      - 7
+    ignore:
+      - goos: darwin
+        goarch: 386
+      - goos: linux
+        goarch: arm
+        goarm: 7
+sign:
+  artifacts: checksum
+archives:
+  -
+    replacements:
+      darwin: Darwin
+      linux: Linux
+      windows: Windows
+      386: i386
+      amd64: x86_64
+checksum:
+  name_template: 'checksums.txt'
+snapshot:
+  name_template: "{{ .Tag }}-next"
+changelog:
+  sort: asc
+  filters:
+    exclude:
+    - '^docs:'
+    - '^test:'