tools: FEATURE.yaml meta-data infrastructure

tools: FEATURE.yaml meta-data infrastructure

Add tooling for feature metadata configuration files.
The main tool is in src/scripts/fts.py

make checkfeaturelist to validate against schema.
make featurelist to dump all feature lists to stdout.

Example feature definition:

name: IP in IP tunnelling
maintainer: Ole Troan <ot@cisco.com>
features:
  - IPv4/IPv6 over IPv4/IPv6 encapsulation:
    - Fragmentation and Reassembly
    - Configurable MTU
    - Inner to outer Traffic Class / TOS copy
    - Configurable Traffic Class / TOS
  - ICMPv4 / ICMPv6 proxying
  - 6RD (RFC5969):
    - Border Relay

description: "Implements IP{v4,v6} over IP{v4,v6} tunnelling as
              described in RFC2473. This module also implement the border relay of
	      6RD (RFC5969)."

state: production
properties: [API, CLI, STATS, MULTITHREAD]
missing:
  - Tunnel PMTUD
  - Tracking of FIB state for tunnel state
  - IPv6 extension headers (Tunnel encapsulation limit option)

JSON schema is embedded in fts.py

Example markdown: https://github.com/otroan/scratch/blob/master/features.md

Change-Id: I903b4ee6b316a9378c259e86dc937092e5d4b7da
Type: make
Signed-off-by: Ole Troan <ot@cisco.com>