Fix jsx examples

[brodybits]

Fixes for JSX examples

• Mark JSX examples as JSX (highlighting)
• fix child elements examples as described below

Additional documentation fix included

• cleanup (remove) trailing whitespace from README.md (updated in a force push)
• UPDATED: added spacing after jsx examples
• UPDATED: added fix to pointer to CodePen demo

Child elements example fixes

I found the following sample line to be confusing:

var span = <span>a dynamic child</span>,
    // ...

(the span var itself does not seem to be a dynamic child element)

proposed change in this PR to read as follows:

var span = <span>child of a dynamic div</span>,
    // ...

Other child element fixes proposed in this PR:

• clarify static span child vs static child div text in the child elements example
• split static & dynamic child examples into separate jsx blocks

[brodybits]

I just force-pushed the following updates:

• fix description "cleanup remove trailing whitespace" commit
• removed 3 more instances of trailing whitespace that I missed the first time
• marked one more jsx example as jsx that I missed the first time

P.S. I also added a couple more changes to add spacing after jsx examples and fix pointer to CodePen demo.

[adamhaile]

Thanks again, Chris, for taking a close look at the README. I'm still thinking about some of your other suggested changes. I may do a pass with some revisions, and would love your opinions after that.

[brodybits]

Thanks for merging