Add only() method for creating Key instance

[irgaly]

Adds only() method to create only Key.

usage

store.openCursor(only(...)).collect {
    ...
}

Though openCursor(only(...)) is almost same as openCursor(Key(...)), It's confusing if only() method is absent.

[cedrickcooke]

Looks like the build failure right now is just a missing comma, should be fixable with ./gradlew formatKotlin.

[irgaly]

Thanks! I have commited the fix to apply formatKotlin.