[Issue #40] Separate whole gem into `adhoq-core` and `adhoq-rails`

[joker1007]

cf. #40

this PR separates gem into adhoq-core and adhoq-rails adhoq-core has only SQL Execution and Reporting Library. adhoq-rails has Rails Engine and depends on adhoq-core

And adhoq is aggregation gem. it is depends on adhoq-core and adhoq-rails both.

Now, Travis CI config and Rake task is a little hacky and not inefficient. In near future, I want to separate repository too and refactor more codes.

Travis sample is here (https://travis-ci.org/joker1007/adhoq).