Improve grammatical consistency and formatting of README.md.

1. Instances of "ARCHIVE_DB.pl" are now "`ARCHIVE_DB.pl`".

2. All flags and properties are codified in the table.

3. All indented `<pre>`s have been converted to fenced ones, so that appropriate syntax highlighting can be appended, which it has been.

4. All lists utilise consistent spacing, which not solely makes them readable in plain text, but also makes the indented ones a lot more readable when rendered.

5. Hyphen-minuses, misused as en dashes, are now en dashes.

6. Erroneously absent commas have been added where required.

7. The table has been prettified for plain text, somewhat.

Author: roke-julian-lockhart