Send the default headers in OAuth as well
Add new timezone field to organisation record

Xero added a timezone field to the organisation object, recently.
Merge pull request #153 from warrenchaudhry/add_archive_status_to_contacts

Add Archive Status to Contacts
Merge pull request #150 from clodeindustrie/patch-1

Add Timezone Field to Organisation
Merge pull request #154 from warrenchaudhry/add_archive_status_to_contacts

Change ARCHIVE Status to ARCHIVED
Merge pull request #155 from warrenchaudhry/add-include-archived-params

Add include_archived Params for Contacts
Add datetime_utc type to http_proxy

This allows fields of type datetime_utc to be used in where clauses.
The datetime_utc type was added in commit
cdae18e1694e3ce6aa9d333f3443f6d4591ad283 but was never added to
base_model_http_proxy, so you get empty where conditions when you
try to filter on fields of that type. This commit fixes that.
Merge pull request #157 from FiguredOnFarm/add-datetime-utc-field-type

Add datetime_utc Type to http_proxy
Fixes creation of TaxRates

Before, there was no primary key defined for TaxRates, so attempting to
create one resulted in the following exception:

```
TypeError: nil is not a symbol
xeroizer/lib/xeroizer/record/base.rb:52:in `[]'
xeroizer/lib/xeroizer/record/model_definition_helper.rb:88:in `id'
xeroizer/lib/xeroizer/record/base.rb:78:in `new_record?'
xeroizer/lib/xeroizer/record/base.rb:101:in `save'
```

This stemmed from being unable to query whether the TaxRate being
created was truly a `new_record?` or not.
Merge pull request #149 from tradegecko/oauth-header

Send the default headers in OAuth as well
Merge pull request #163 from chargify/tax_rates

Fixes Creation of TaxRates
get invoice line items summary when doing Invoice.all with page request
update readme