Function: check_spelling

--Usage--
> check_spelling(some_tagged_string,  language:language_code)

Check the spelling of a piece of text, and mark errors with @<error-spelling>@ tags.

--Dictionaries--
The language code must correspond to a dictionary in the @dictionaries@ data directory (usually @%MSE_DIR%\data\dictionaries@).
A dictionary consists of two files, @language.dic@ and @language.aff@.

Magic Set Editor is compatible with Hunspell dictionaries, which are also used by Open Office and Firefox.
These dictionaries can be found on [[http://wiki.services.openoffice.org/wiki/Dictionaries|the Open Office website]].

--Parameters--
! Parameter	Type			Description
| @input@	[[type:tagged string]]	String to check.
| @language@	[[type:string]]		Language code.<br/>
		 			The language code consists of an [[http://en.wikipedia.org/wiki/ISO_639|ISO language code]] and an [[http://en.wikipedia.org/wiki/ISO_3166-1|ISO country code]] separated by an underscore.
| @extra_dictionary@	[[type:string]] (optional)
			 		Name of an additional dictionary to use. This dictionary could be specific to the game file.
			 		The name should be of the form @"my-game.mse-game/dictionary"@,
			 		in which case MSE looks for the file @"my-game.mse-game/dictionary.en_US.dic"@ where @"en_US"@ is the language code.
| @extra_match@	[[type:function]] (optional)
		 			Function that returns @true@ for additional words that are spelled correctly.
		 			This can be used for codes like @"+1/+1"@ on magic cards.

--Examples--
> check_spelling("Can I have an appple?", language:"en_US")
>   == "Can I have an <error-spelling:en_US>appple</error-spelling:en_US>?"

In the second example any text matching the [[type:regex]] @"x[a-z]*"@, i.e. any word beginning with the letter x, is not considered an error:
> check_spelling("xyzzyx", language:"en_US")
>   == "<error-spelling:en_US>xyzzyx</error-spelling:en_US>"
> check_spelling("xyzzyx", language:"en_US", extra_match: match@(match:"x[a-z]*"))
>   == "xyzzyx"