This enables users of the bio-rd library to reuse the state numbering.
Otherwise users have to maintain their own constats to avoid magic
numbers.

* first steps to metrics

* next small step

* fixed tests

* added comments

* postponed RouterAccepted and RoutesRejected to next step

* read update counters

* added test

* added missing test file

* Route not used any more

* added metrics for session state and time since establish

* increased test coverage, time since establish impl.

* added prom collector

* added metrics endpoint to BGP example

* added metrics for VRF

* removed commented metrics

* fixed logging inconsistency in example

* Update main.go

* gofmt

* fixed typo

* sane default for ClientOptions, otherwise max paths for non add path is 0

* applied new default to BMP test

* added regression test

* Fix FSM Address Family Init

* Adding tests for fix

* Fix build

* Fix build

* Adding support for dumping BGP RIBin & RIBout

* Fix build

* Add API Server to BGP IPv4 example

* Re-factored Route dumping API to use streaming RPC

* Add benchmark

* Get rid of holdtimer as a timer

* Fix tests

* Completing benchmark

* Fix atomic stuff

* added unique name for locRIBs

* added VRFs

* added error when no RIB configured in VRF

* vrf unique name ensurance

* fixed examples

* added missing test

* for convenience we provide a default RIB for v4 and v6 on each VRF

* removed debug output in main.go (api is coming)

* also removed debug output from fib example

* removed fib example

* replaced sync.Map with own type

* fixed map test

* Fix cease after bad peer AS

* Fix test

Package errors provides simple error handling primitives.
Read more on https://github.com/pkg/errors

This reverts commit 1baef567.

this makes it unnecessary to cast it to int when calling the netlink API

This reverts commit a5bccc29, reversing
changes made to 88c1c813.