Added no_trailing_whitespace.allowed_in_comments rule option. fixes clutchski/coffeelint#45

I don't think most projects use markdown or docco in comments, so this
rule is off by default (backward compatible).
Added an exception to exclude errors caused by long URLS in comments.
Added a check to find duplicate keys defined on classes and objects.
Merge pull request #91 from AsaAyers/trailing-space-45

Added no_trailing_whitespace.allowed_in_comments rule option.
Merge pull request #92 from AsaAyers/duplicate-key

Added a check to find duplicate keys defined on classes and objects.
Merge pull request #93 from AsaAyers/line-length-exception

Added an exception to exclude errors caused by long URLS in comments.