Create an Observable that emits each char in the source String.
rename `from(String)` to `byCharacter(Observable<String>)` to better match byLine.
removed the `Line` class because can be better done with `zip(Observable.range(0, MAX_INT), byLine(src), func2)`
Merge pull request #1 from abersnaze/observable_from_string

A few changes to make it mesh better.
Merge pull request #5 from lucaslabs/observable_from_string

Create an Observable that emits each char in the source String.