Add compiler options: showDeprecation/showWarnings/-Xlint
Suppress Seq.of(T...) warnings due to varargs
Suppress or fix warnings: unchecked, rawtypes, serial
cleanups

* optimize imports
* use method reference
* remove redundant initializer
Add Seq<T> Seq.seq(Optional<T>)
Merge pull request #66 from kxbmap/suppress-warnings

Suppress or fix warnings
Merge pull request #67 from kxbmap/optional-seq

Add Seq<T> Seq.seq(Optional<T>)