Adding dictionary for Arabic

[msalhab96]

I used the Arabic dataset provided by opus to create an Arabic dictionary for the Arabic language, in this pull request I've made the following:

• Added the frequency dictionary to resources.
• Added the original/full data to data/
• Added ar_exclude and ar_include to data/
• modified the supported languages by adding ar
• modified the README file by adding an Arabic spell checker and added Arabic to the supported languages.

I have tested the code and it works, here's an example

from spellchecker import SpellChecker

spell = SpellChecker(language='ar')

# find those words that may be misspelled
misspelled = spell.unknown(["اذلهب", "كتا", "اساح"])

for word in misspelled:
    print(word)

    # Get a list of `likely` options
    print(spell.candidates(word))

    # Get the one `most likely` answer
    print(spell.correction(word))