Anycast-healthchecker

* Add a note for bird\_conf setting
* Keep a history of changes for bird configuration
* Add support for specifying a single service check

* Remove die parameter from get\_ip\_prefixes\_from\_bird
* Remove unnecessary call to rstrip function
* Use ConfigParser method to fetch configuration
* Don't exit when there aren't any service checks
* Make the use of format consistent in multi-line
* Add support for removing IP-Prefixes without a check
* Move functions to utils module
* Use double quotes silence error with bash 4.4 version

* Include IP address and prefix length in JSON blob

* Rephrase sentences and fix typos in README
* Restructure documentation about settings in README
* Add option to disable the IP assignment check
* Simplify sanity check on configuration
* Log stderr and stdout of check cmd when it fails
* Rephrase some comments
* Add Documentation option in the Systemd unit file

* Set more accurate sleep time to avoid interval drifting
* Add contrib dir and move files there

* Remove inaccurate note from README
* Catch the case where check\_cmd can't be killed
* Skip string formatting operation