Add as-fuzzy command line argument to mark translated messages as fuzzy for future review.

[r12f]

Before the change:

#: src/SUMMARY.md:3
msgid "This is a pen!"
msgstr "This is a pen!"

After enabling --fuzzy:

#: src/SUMMARY.md:3
#, fuzzy
msgid "This is a pen!"
msgstr "This is a pen!"

[r12f]

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