Implements splicetext() and splicetext_char()

[amylizzle]

Fixes #356 by implementing splicetext and _char variant Tests for same.

Note: This is more permissive than DM's default because it doesn't throw a compile error for a number of test cases that frankly don't need to. These guys will throw compile errors in DM but not OD:

    splicetext("abcdef", 4, Insert="test") //expected 2 to 4 arguments    
    splicetext("abcdef", Insert="") //expected 2 to 4 arguments
    splicetext("abcdef") //expected 2 to 4 arguments

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This pull request has conflicts, please resolve those before we can evaluate the pull request.