specs: test Puppet 3.1.0, only set libdir where required

Bump puppetlabs_spec_helper for #18165, fixes 3.1.0 libdir initialisation
Rename 'licence' so Puppet Forge finds it
Implement prefetch in host provider
Implement prefetch in mailalias provider
sshd_config: Simplify type and provider with key as namevar
Ignore rvm/rbenv configs
Remove symlinks from docs/, fixes #25
Link to examples from README
Release 0.5.2
Merge branch 'master' of github.com:camptocamp/puppet-augeasproviders
Merge branch 'master' of github.com:hercules-team/augeasproviders