Fixes to Spree::TaxCloud#destination_address

* Refer to ::TaxCloud::Address rather than TaxCloud::Address
* taxcloud_usps_user_id.present? because it can be ""
* TaxCloud::Address is initialized with lowercase symbols
Merge pull request #18 from freerunningtechnologies/destination_address

Fixes to Spree::TaxCloud#destination_address
Fix removing items from cart when tax adjustment exists.
Merge pull request #29 from jdutil/master

Fix removing cart items.
Fix precision, scale of decimal columns

The columns were originally created with precision=8 scale=5, which does
not allow prices greater than 999.

This changes
* price to the same as line_item_price (precision=8 scale=2)
* ship_total to the same as adjustment (precision=10 scale=2)
* amount to precision=13 scale=5, which can fit the maximum allowable
  amount of either column at 5 decimal places of precision.