Add MemInfo to the system pkg.

MemInfo provides a simple API to get memory information from the
system.

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

system/meminfo.go

@@ -0,0 +1,17 @@
+package system
+
+// MemInfo contains memory statistics of the host system.
+type MemInfo struct {
+	// Total usable RAM (i.e. physical RAM minus a few reserved bits and the
+	// kernel binary code).
+	MemTotal int64
+
+	// Amount of free memory.
+	MemFree int64
+
+	// Total amount of swap space available.
+	SwapTotal int64
+
+	// Amount of swap space that is currently unused.
+	SwapFree int64
+}