First steps towards making the lexer stream tokens
Stream tokens when lexing.

Instead of returning the tokens as a whole they are now streamed using
XML::Lexer#advance. This method returns the next token upon every call. It uses
a small buffer in case a particular block of text results in multiple tokens.
Updated the lexer benchmarks.

These had to be updated for the API changes of Oga::XML::Lexer.
Basic benchmarks for the Parser class.
Truncate lines in parser errors.

The offending lines of code displayed in the error message are truncated to 80
characters. This should make reading the error messages less of a pain when
dealing with very long lines of HTML/XML.
Lex attributes with namespaces.

These are lexed as just the name instead of two separate tokens.
Use a Set for storing void element names.
Replaced the HRS fixture with one from Gist.

The HRS output is invalid, which Oga can not handle at this time.