Split qmynd into qmynd and qmynd-impl. This is presently a no-op as
neither package exports anything yet, but that will change soon.

• Split PARSE-DECIMAL out to utilities.lisp

• Use column-definition charset encoding options for parsing strings
  in binary protocol; fallback to connection charset.

• Rewrite binary integer parsing to use common helper function, rely
  on basic-types signed integer parsing based on column-defintion
  unsigned flag.