Support for named fields in operation signatures

[SamCooper]

Arguments to MAL operations can now be specified as named fields rather than just type information, i.e. from this:

<mal:submit>
  <mal:type name="Boolean" area="MAL"/>
  <mal:type list="true" name="InstanceBooleanPair" area="COM"/>
</mal:submit>

to this:

<mal:submit>
  <mal:field name="isGroupIds">
    <mal:type name="Boolean" area="MAL"/>
  </mal:field>
  <mal:field name="enableInstance">
    <mal:type list="true" name="InstanceBooleanPair" area="COM"/>
  </mal:field>
</mal:submit>

The name should be reflected in the generated API, especially in the get/set methods in the compound return classes.