Fix docs: `dt-init dom` related properties update
Dev - Markdown: Add class for <img> elements created in Markdown for styling
Dev: Modify the API extender to remove a potential closure issue

Dev: Modify the initialisation of _Api - the old method of using `=`
twice on a row caused Chrome's debugger to show it as both names
concatinated which was confusing.

Fix: Remove API "build" code. That was part of the API prototype and the
design moved away from that approach. The code was redundant and unused.
Fix: Memory leak with child rows in a table that is destroyed
New: `dt-api row().child.remove()` and `dt-api row().child().remove()` methods to provide the ability to remove and destroy child rows
Fix docs: Note that the row().child() method's return value can have an effect on the chaining

* This fixed DataTables/DataTables issue #326.
* Special thanks to `Scottmitch1` (on github) for help with this one!