split into smaller components

[hadeeb]

Splits the component into smaller component for each hydration strategy.
closes #14

Notes on hydration when visible

To support IntersectionObserver customizations, an IntersectionObserver instance is created for each component unique set of IntersectionObserver options.
As an alternative to this, the component can accept a custom IntersectionObserver instance like this. It could be beneficial if there is a list of components to be hydrated in a same way or the user needs more control on hydration.

[hadeeb]

Name of exported components could be improved.
The readme also has to be updated to reflect these changes.

[nilanjansiromani]

@hadeeb Can you check if phantomJS will support this
Some legacy codes use Phantomjs still as the unit test driver

[nilanjansiromani]