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 df4bf05323ccf9bdda85325bd8431f9a0b134fcc on DhiaEddineSaidi:tagNameToLowerCaseOption into f0b870011b84da362c863dc914157f30d4a603ac on andrejewski:master.

[andrejewski]

See https://github.com/andrejewski/himalaya/issues/55#issuecomment-321808564.

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.