Use pwd as a workspace; move sources to src/gopheros and rewrite imports

By setting up pwd as a Go workspace, we can trim import paths from
something like "github.com/achilleasa/gopher-os/kernel" to just
"kernel".

These changes make forking easier and also allows us to move the code to
a different git hosting provider without having to rewrite the imports.

src/gopheros/kernel/mem/size.go

@@ -0,0 +1,12 @@
+package mem
+
+// Size represents a memory block size in bytes.
+type Size uint64
+
+// Common memory block sizes.
+const (
+	Byte Size = 1
+	Kb        = 1024 * Byte
+	Mb        = 1024 * Kb
+	Gb        = 1024 * Mb
+)