Fix format, rendering, typos, syntax, content in manuals.

- Fix Markdown syntax.
- Fix code rendering.
- Sync content between manual and manual-premium. (Attempted to take the more recent pieces from each.)
- Fix capitalisation of headings.
- Fix capitalisation of abbreviations: XML, HTML, JSON, GCC.
- Fix capitalisation of Cppcheck in prose.
- Remove trailing spaces.
- Fix missing commas after "If", "To".
- Other English syntax fixes.
- "etc" -> "etc."
- "...." -> "..."

Author: vkucera