Cease stripping the final newline in generated Markdown

[matta]

This change moves the code closer to org-md-inner-template, which has similar logic but doesn't call org-trim.

• ox-hugo.el (org-hugo-inner-template): Remove call to org-trim to address github issue #671. Users no longer need to set require-final-newline to t to get a final newline, and users with that set to ask no longer get prompted on every save.
• ox-blackfriday.el (org-blackfriday-inner-template): ditto.

[kaushalmodi]

@matta Thanks. I have manually merged this in https://github.com/kaushalmodi/ox-hugo/commit/8fbd301c03296253bfb5ee193770e1da3ea2df1a after adding few test fixes.