GH-15: flag words as rare instead of bad in NeoVim

This change marks all words in all dictionaries as rare words so that
NeoVim highlights them as SpellRare instead of SpellBad.  This lets you
distinguish between wordy writing and normal misspellings, respectively.

In order for this to work, your NeoVim needs to be patched as follows:

  https://github.com/neovim/neovim/pull/2456

  https://groups.google.com/forum/#!topic/vim_dev/rPWOoR3ZgSA

See `:help spell-wordlist-format` for details about dictionary markings.

data-neovim/en/problematic.dic

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+# http://www.dailywritingtips.com/50-problem-words-and-phrases/
+/encoding=utf-8
+a lot/?
+a while/?
+ability/?
+able/?
+actual/?
+actually/?
+advice/?
+advise/?
+affect/?
+affects/?
+all right/?
+all together/?
+alot/?
+alright/?
+also/?
+although/?
+altogether/?
+amend/?
+among/?
+amount/?
+any way/?
+anyway/?
+anyways/?
+assume/?
+assumes/?
+assumption/?
+assure/?
+awhile/?
+because/?
+between/?
+biannual/?
+biennial/?
+bring/?
+cache/?
+cachet/?
+can/?
+capability/?
+capable/?
+compare to/?
+compare with/?
+complement/?
+compliment/?
+compose/?
+composed/?
+comprise/?
+comprises/?
+conform to/?
+conform/?
+connote/?
+consist of/?
+consist/?
+consists/?
+constitute/?
+continual/?
+continuous/?
+convince/?
+credible/?
+credulous/?
+data/?
+datum/?
+denote/?
+desert/?
+deserts/?
+dessert/?
+desserts/?
+different from/?
+different than/?
+different to/?
+discreet/?
+discrete/?
+each other/?
+economic/?
+economical/?
+effect/?
+effects/?
+elemental/?
+elementary/?
+emend/?
+emigrate/?
+emigration/?
+endemic/?
+enquire/?
+enquiry/?
+ensure/?
+envy/?
+epidemic/?
+farther/?
+fewer/?
+flammable/?
+forego/?
+forgo/?
+further/?
+gibe/?
+healthful/?
+healthy/?
+hilarious/?
+historic/?
+historical/?
+home in/?
+hone in/?
+hysterical/?
+if/?
+immigrate/?
+immigration/?
+inflammable/?
+inquire/?
+inquiry/?
+insure/?
+irregardless/?
+jealousy/?
+jibe/?
+jive/?
+lay/?
+leach/?
+leech/?
+less/?
+libel/?
+lie/?
+literal/?
+literally/?
+loose/?
+lose/?
+math/?
+maths/?
+may/?
+might/?
+more/?
+nauseated/?
+nauseous/?
+nonflammable/?
+notable/?
+noteworthy/?
+noticeable/?
+number/?
+one another/?
+oral/?
+over all/?
+over/?
+overall/?
+pandemic/?
+partially/?
+partly/?
+peak/?
+people/?
+persons/?
+persuade/?
+pique/?
+predominantly/?
+predominately/?
+presume/?
+presumes/?
+presumption/?
+purposefully/?
+purposely/?
+regretfully/?
+regrettably/?
+repetitious/?
+repetitive/?
+say/?
+sensual/?
+sensuous/?
+since/?
+slander/?
+stationary/?
+stationery/?
+take/?
+tell/?
+than/?
+that/?
+their/?
+then/?
+there/?
+they're/?
+they’re/?
+to/?
+too/?
+tortuous/?
+torturous/?
+transcript/?
+transcription/?
+up on/?
+upon/?
+verbal/?
+whereas/?
+whether/?
+which/?
+while/?
+who/?
+whom/?
+wreak/?
+wreck/?