Merge pull request #139 from khwon/develop

v0.1.1
Merge pull request #140 from khwon/develop

v0.1.2
Merge commit '221baca02ae4a0d20896b59e6adcc8b17a6730e3'
fix invalid query in pg

.first appends order by posts.id limit 1, which causes
error in postgresql.
To retrive first element in Relation without modifying query,
[0] should be used.
Merge branch 'hotfix/fixpost'
Merge tag 'fixpost' into develop

v0.1.3.1