Updating build.sh to work on Mono
MQ: Cleanup to use var
Make TagHelperOutput.Attributes case insensitive.

- Changed the Attributes dictionary to utilize a StringComparer.OrdinalIgnoreCase comparer.
- Changed TagHelperExecutionContext to ignore attribute casing.
- Updated the AllAttributes and HtmlAttributes dictionaries to ignore attribute casing.
- Added tests to validate their new behavior.

#186