Revise documentation for Amazon::MWS::Client

[rabbiveesh]

I just started working with this library now. I would love to help out with this.

[racke]

@rabbiveesh That would be great. I already started adding a API Support section:

diff --git a/lib/Amazon/MWS/Client.pm b/lib/Amazon/MWS/Client.pm
index d8b6d9a..3350e68 100644
--- a/lib/Amazon/MWS/Client.pm
+++ b/lib/Amazon/MWS/Client.pm
@@ -157,6 +157,28 @@ this exception will be thrown.  The response can be found in $e->response.

 The LWP::UserAgent object used to send the requests to Amazon.

+=head1 API SUPPORT
+
+=head2 Easy Ship
+
+The Easy Ship API applies only to sellers in India and is B<not supported>.
+
+=head2 Feeds
+
+The L<Feeds API|https://docs.developer.amazonservices.com/en_US/feeds/Feeds_Overview.html> is supported by L<Amazon::MWS::Feeds>.
+
+=head2 Finances
+
+The L<Finances API|https://docs.developer.amazonservices.com/en_US/finances/Finances_Overview.html> is supported by L<Amazon::MWS::Finances>.
+
+=head2 Fulfillment Inventory
+
+The L<Fulfillment Inventory|https://docs.developer.amazonservices.com/en_US/fba_inventory/FBAInventory_Overview.html> is supported by L<Amazon::MWS::FulfillmentInventory>.
+
+=head2 Orders
+
+Supported by L<Amazon::MWS::Orders>.
+
 =head1 API METHODS

 The following methods may be called on objects of this class.  All concerns