CODING_STYLE: Fence code samples, fix tab breakage

The formatting of CODING_STYLE.md was rather off due to some MarkDown syntax errors ­— most egregiously, because the first code block was (a) enclosed in a bullet list item, and (b) partly indented with tab characters, not spaces, it failed to display as a code block, and instead wrapped to one long line of body text.

This PR ensures that all of the code samples are recognized as pre-formatted blocks, either by increasing the indent level of the text as necessary, or explicitly fencing. (Primarily the latter, to also activate syntax highlighting.

In addition, some very minor changes to the content are made, primarily to increase consistency in how various style guidelines are expressed/demonstrated.