Implement Character::NotificationTexts endpoint

[amclain]

The scope of this issue is to implement the Character::NotificationTexts endpoint.

[amclain]

This endpoint has a CDATA section that needs to be coerced. The CDATA params change based on the type of message.

<rowset name="notifications" key="notificationID" columns="notificationID">
  <row notificationID="589251502">
    <![CDATA[amount: 43188
billTypeID: 2
creditorID: 1000033
currentDate: 131241741999174933
debtorID: 98063277
dueDate: 131267637960000000
externalID: 27
externalID2: 60003652
]]>
  </row>
</rowset>

[amclain]

This problem may be solvable with the :hash type, which is being introduced in PR #159. Although it won't coerce the individual values (it may be impractical to coerce every possible type of CDATA), it can structure the CDATA element as a Ruby hash so the user can sort through the data.