Adding option to prevent tagnames from beeing lowercase.

[DhiaEddineSaidi]

Example << Angular components html templates >> need to preserve the case of the components tags(selectors)

[coveralls]

Coverage remained the same at 100.0% when pulling df4bf05 on DhiaEddineSaidi:tagNameToLowerCaseOption into f0b8700 on andrejewski:master.

[andrejewski]

See #55 (comment).

I am against changing what tagName means in the current spec. Maybe we can add a rawStartingTagName and rawClosingTagName fields to the output as was done for position information.

The option name will have to change to be false by default, so something like includeRawTagNames.

Changing the meaning of voidTags such that if someone wanted proper semantics for img tags they would have to include all cases is not something to support.