[ABW]: added author validation and removed overlap from paging in...

[ABW]: added author validation and removed overlap from paging in get_discussions_by_author_before_date
added validation of truncate_body parameter to every call that has it
unified tag validation and fixed null limit problem in get_discussions_by_blog
added truncate_body parameter to get_discussions_by_author_before_date because it is present in all similar calls