ENH: Simplify JSON/Dictionary parsing logic

[rmhowe425]

• Closes out ENH: Simplify JSON & Dictionary parsing logic #216
• Replacing multi-conditional look-ahead checks and implicit dictionary key references with dict.get().

Implementation in PR follows best practices mentioned here, and also improves code readability.

[rmhowe425]

@achillean Submitting a PR if interested!

There are a few other places in the code where dict.get() could be used to simplify the code, as mentioned in my reference to a open PR. I left this for the author of the PR to address if they want.