v0.2.0

multiple improvements in scope of TEC-5757:

• added .gitignore
• stop using glide, instead use go modules
• improved logging
• changed the way prometheus metrics work, we used to export 0 for up and 1 for down. now it works vice versa, complies with exporter convention
• changed logging library to use more something more lightweight
• use flag library from stdlib instead of kingpin. it is deprecated
• introduced scrape_error metric for exporter errors
• deleted .goreleaser.yml and .travis.yaml (they were not used)
• updated Dockerfile, README.md and systemd.service example accordingly
• try collecting replication metrics only if the role is replica