Fixes to language documentation

- Use backticks consistently for inline code
- Capitalize section headers and proper nouns
- Minor grammatical fixes
Fixes to contributor module documentation

- Changed "Contrib" to "Contributor"
- Fixed mismatched inline code in list* usage
- Added missing hyperlink targets
Change documentation code block language to Hy
Adhere to CPython's documentation guidelines

- Inline code is written using ``double backticks``
- Italicized text uses *asterisks* rather than `single backticks`
- Function parameters are italicized rather than written as inline code
Merge pull request #704 from iKevinY/doc-changes

Fixes to documentation (language & contributor modules)