embedded stdlib

This PR embeds the stdlib into the dagger binary itself for convenience.
Long term we will want to source the stdlib directly from git.

- Updated go to 1.16 to use the new built-in embedding functionality
- The `stdlib` go package now contains an embed of the stdlib

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

stdlib/dagger/dagger.cue

@@ -0,0 +1,61 @@
+package dagger
+
+// Any component can be referenced as a directory, since
+// every dagger script outputs a filesystem state (aka a directory)
+#Dir: #dagger: compute: [...#Op]
+
+// One operation in a script
+#Op: #FetchContainer | #FetchGit | #Export | #Exec | #Local | #Copy | #Load | #Subdir
+
+// Export a value from fs state to cue
+#Export: {
+	do: "export"
+	// Source path in the container
+	source: string
+	format: "json" | "yaml" | *"string"
+}
+
+#Local: {
+	do:      "local"
+	dir:     string
+	include: [...string] | *[]
+}
+
+// FIXME: bring back load (more efficient than copy)
+
+#Load: {
+	do:   "load"
+	from: _
+}
+
+#Subdir: {
+	do:  "subdir"
+	dir: string | *"/"
+}
+
+#Exec: {
+	do: "exec"
+	args: [...string]
+	env?: [string]: string
+	always?: true | *false
+	dir:     string | *"/"
+	mount: [string]: "tmp" | "cache" | {from: _, path: string | *"/"}
+}
+
+#FetchContainer: {
+	do:  "fetch-container"
+	ref: string
+}
+
+#FetchGit: {
+	do:     "fetch-git"
+	remote: string
+	ref:    string
+}
+
+#Copy: {
+	do:   "copy"
+	from: _
+	src:  string | *"/"
+	dest: string | *"/"
+}