title: UnicodeError with SqlAlchemy + Firebird + FDB
body: <p>I'm triying to display results from a firebird 3.x database, but get:</p>
  
  <blockquote>
    <p>File
    "/...../Envs/pos/lib/python3.6/site-packages/fdb/fbcore.py",
    line 479, in b2u
        return st.decode(charset) UnicodeDecodeError: 'utf-8' codec can't decode byte 0xd1 in position 9: invalid continuation byte</p>
  </blockquote>
  
  <p>Despite I set utf-8 everywhere:</p>
  
  <pre><code># -- coding: UTF-8 -- 
  
  import os
  
  os.environ["PYTHONIOENCODING"] = "utf8"
  
  from sqlalchemy import *
  
  SERVIDOR = "localhost"
  BASEDATOS_1 = "db.fdb"
  
  PARAMS = dict(
      user="SYSDBA",
      pwd="masterkey",
      host="localhost",
      port=3050,
      path=BASEDATOS_1,
      charset='utf-8'
  )
  
  firebird = create_engine("firebird+fdb://%(user)s:%(pwd)s@%(host)s:%(port)d/%(path)s?charset=%(charset)s" % PARAMS, encoding=PARAMS['charset'])
  
  def select(eng, sql):
      with eng.connect() as con:
          return eng.execute(sql)
  
  for row in select(firebird, "SELECT * from clientes"):
      print(row)
  </code></pre>