Content additions

• and.md / or.md: Added content to match the structure of the rest of the reference section.
• get.md: Added use cases for the get function being similar to the value function.
• Accumulators: Added plain-English descriptions for the Do and While unary forms.
• Glossary: Improved descriptions of infix, postfix and prefix to better understand the differences between each other.
• Argument glosary: Fixed the wrong formula for the right domains of a list of n depth.
• Small typos and consistency issues: e.g -> e.g., doesnt -> does not, etc.