Accept a String or charstring for database open

[warmwaffles]

Closes #278
Closes #277

[warmwaffles]

For some stupid reason, locally my system is failing for

  1) test .connect/1 fails to write a file from URL with mode=ro (Exqlite.ConnectionTest)
     test/exqlite/connection_test.exs:59
     ** (MatchError) no match of right hand side value: {:error, %Exqlite.Error{message: "database_open_failed", statement: nil}}
     code: {:ok, conn} = Connection.connect(database: "file:#{path}?mode=ro")
     stacktrace:
       test/exqlite/connection_test.exs:72: (test)

  2) test .connect/1 connects to a file from URL (Exqlite.ConnectionTest)
     test/exqlite/connection_test.exs:50
     ** (MatchError) no match of right hand side value: {:error, %Exqlite.Error{message: "database_open_failed", statement: nil}}
     code: {:ok, state} = Connection.connect(database: "file:#{path}?mode=rwc")
     stacktrace:
       test/exqlite/connection_test.exs:53: (test)

I need to figure out why.