Support optional charset parameter for full UTF-8 support (utf8mb4)

[clue]

This changeset adds support for an optional charset parameter for full UTF-8 support (utf8mb4).

By default, the connection uses the utf8 charset encoding. Note that
MySQL's utf8 encoding (also known as utf8mb3) predates what is now
known as UTF-8 and for historical reasons doesn't support emojis and
other characters. If you want full UTF-8 support, you can pass the
charset encoding like this:

$factory->createLazyConnection('localhost?charset=utf8mb4');

Resolves / closes #133
Refs #131