v0.5.0

Changelog

cbc2f9b cache dep dependencies
ae524ce cleanup
4a40d73 disable errcheck in tests
b101c56 enable more linters
de7945b fix linter errors
3c7d069 fix panic
ffdb7bf fix panic
3736b1c handle block errors
420e523 no verbose in tests
d3c5016 refactor
2924dad refactor unchoker
0d43525 run choker func
1ba834a switch gometalinter with golangci-lint
07cb2f9 update go version
e3620bb use container based build env
9efe0b6 use xenial environment
6a4787e write tests for info downloader
9f90cf0 write tests for piece downloader