critical fixes for multibyte characters in stream implementation

* There was some logic to handle multibyte characters when split across multiple chunks, but it was lacking.
  * Fixed an issue where if a chunk starts with a multibyte character, the rest of the chunk is discarded.
  * Fixed an issue where if a chunk starts with a single byte character and ends with a partial multibyte character, that character will now be sequenced on the subsequent chunk.
  * Stream now only combines single byte characters and applies multibyte character logic to remaining bytes.
* Extended the generic test engine a bit so that it allows for customized chunking.
* Extended utf8 chunk test so that it covers more scenarios.

Apologies in advance for all of the whitespace changes. I did not realize that I hadn't switched my editor until it was far too late. If this is problematic, I can circle back.
@davidgwking why is this test value and the one on line 68 also changed?