Merge scalikejdbc-interpolation-core into scalikejdbc-core

We already dropped Scala 2.9 support since ScalikeJDBC 2.0.0 release. Now we don't need to separate scalikejdbc-interpolation-core library from scalikejdbc-core. Thank you for @xuwei-k's suggestion and implementation.

#### 2.1.2

```
| +-org.scalikejdbc:scalikejdbc_2.11:2.1.2
| | +-org.scalikejdbc:scalikejdbc-core_2.11:2.1.2
| | |
| | +-org.scalikejdbc:scalikejdbc-interpolation_2.11:2.1.2
| |   +-org.scalikejdbc:scalikejdbc-interpolation-core_2.11:2.1.2
| |   | +-org.scalikejdbc:scalikejdbc-core_2.11:2.1.2
| |   |
| |   +-org.scalikejdbc:scalikejdbc-interpolation-macro_2.11:2.1.2
| |   | +-org.scalikejdbc:scalikejdbc-interpolation-core_2.11:2.1.2
| |   |   +-org.scalikejdbc:scalikejdbc-core_2.11:2.1.2
```

#### 2.1.3

```
| +-org.scalikejdbc:scalikejdbc_2.11:2.1.3
| | +-org.scalikejdbc:scalikejdbc-core_2.11:2.1.3 (merged)
| | |
| | +-org.scalikejdbc:scalikejdbc-interpolation_2.11:2.1.3
| |   +-org.scalikejdbc:scalikejdbc-interpolation-core_2.11:2.1.3 (empty, deprecated)
| |   | +-org.scalikejdbc:scalikejdbc-core_2.11:2.1.3 (merged)
| |   |
| |   +-org.scalikejdbc:scalikejdbc-interpolation-macro_2.11:2.1.3
| |   | +-org.scalikejdbc:scalikejdbc-interpolation-core_2.11:2.1.3 (empty, deprecated)
| |   |   +-org.scalikejdbc:scalikejdbc-core_2.11:2.1.3 (merged)
```

#### 2.2.x

```
| +-org.scalikejdbc:scalikejdbc_2.11:2.2
| | +-org.scalikejdbc:scalikejdbc-core_2.11:2.2
| | |
| | +-org.scalikejdbc:scalikejdbc-interpolation_2.11:2.2
| |   +-org.scalikejdbc:scalikejdbc-core_2.11:2.2
| |   |
| |   +-org.scalikejdbc:scalikejdbc-interpolation-macro_2.11:2.2
| |   | +-org.scalikejdbc:scalikejdbc-core_2.11:2.2
```