Release 1.6.0 of bmv2

• action primitives have access to corresponding P4Objects for implementation
• support for parser errors and parser verify statements (P4_16)
• support for comparing header instances in expressions in JSON input
• action primitives can take strings as parameters
• support for enums (P4_16)
• ability to start a switch target binary without providing a JSON input
• provided meter implementation supports color-awareness
• some code cleanup (mostly include directives)