Fix bug in PlatyPS New-MarkdownHelp with multi-line param descriptions (?and example help maybe affected also?).

[IMJLA]

When provided the same comment-based help as input, Get-Help respects the line breaks but New-MarkdownHelp does not.
New-MarkdownHelp generates an inaccurate markdown representation by converting multiple lines to a single line.
Declared as wontfix PowerShell/platyPS#314
Want to fix it myself and submit a PR
Until then, workaround is to include markdown syntax in PowerShell comment-based help
That is why there are so many extra blank lines and unordered lists in the commented metadata in this script