Improve application developer guide documentation

[cazlo]

Is your feature request related to a problem? Please describe.
The application developer's guide markdown is inconsistently communicating function names, sometimes function names use code blocks, while sometimes they do not. Also it contains several minor grammatical errors and typos.

Describe the solution you'd like
Consistently communicate function references in markdown code blocks.
Fix grammatical errors.

Describe alternatives you've considered
N/A

Additional context
N/A

Requester Info
Andrew Paettie, personal contributor