Minimum version is now 1.8 according to build.go (from latest master, cloned a few minutes ago):
```
paul@voga:~/third-dev/restic$ go run build.go
Go version go1.7.4 detected, restic requires at least Go 1.8
exit status 1
```
* convert documentation to reStructuredText
* switch from mkdocs to sphinx
* rewrite README.md (now .rst) to include less information and be more
attractive