Move parsing functions to pkg/parsers and the specific kernel handling

functions to pkg/parsers/kernel, and parsing filters to
pkg/parsers/filter. Adjust imports and package references.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)

parsers/kernel/uname_unsupported.go

@@ -0,0 +1,15 @@
+// +build !linux !amd64
+
+package kernel
+
+import (
+	"errors"
+)
+
+type Utsname struct {
+	Release [65]byte
+}
+
+func uname() (*Utsname, error) {
+	return nil, errors.New("Kernel version detection is available only on linux")
+}