Version 0.4: Introduced per-URL configuration

- [feature] Support per-URL configuration variables e.g. `ghq.<URL>.vcs` to skip VCS backend auto-detection
- [fix] Fixed path problems of SCP-like URLs thanks to @osamu2001 (#20)
- [fix] `ghq get -u` now updates work tree for Mercurial repositories thanks to @troter (#19)
- And typo fixes thanks to @sorah, @dtan4 (#17, #18)