Add avro constructors with Configuration for #295.

To avoid doubling the number of constructors in ParquetWriter, this
creates more defaults that subclasses can use. The new AvroParquetWriter
constructors call the most specific constructor directly and use the
default constants from ParquetWriter to match the default behavior of
its constructors.

Also fixed a few doc mistakes.
Add Configuration constructor in thrift writer for #295.