Milestones
Any ticket can be assigned to a milestone. Milestones can also belong to each other - milestones with a 
parent-id are child milestones.
API URLs
| Data | Method | URL | 
| All milestones | GET | /project/milestones | 
| Create a new milestone | POST | /project/milestones | 
| Update an existing milestone | PUT | /project/milestones/milestone_id | 
Object Properties
GET /project/milestones
<ticketing-milestone>
  <id type="integer">1734</id>
  <name>Example Milestones</name>
  <start-at type="date">2009-09-17</start-at>
  <deadline type="date">2009-11-20</deadline>
  <parent-id type="integer" nil="true"/>
  <estimated-time>15</estimated-time>
  <responsible-user-id>1</responsible-user-id>
  <status>active</status>
</ticketing-milestone>
- idthe unique ID for this milestone
- namethe milestone name as entered in the interface
- start-atthe date this milestone begins. Format: yyyy-mm-dd
- deadlinethe date of this milestone's deadline. Format: yyyy-mm-dd
- parent-idthe ID of this parent's milestone
- estimated-time- The estimated time for this milestone.
- statusthe milestone status. One of- active,- completedor- cancelled.
- responsible-user-id- the id of the user responsible for the milestone
POST /project/milestones
<ticketing-milestone>
  <name>Example Milestone</name>
  <description>A description for my example milestone</description>
  <start-at type="date">2017-09-06</start-at>
  <deadline type="date">2017-09-12</deadline>
  <parent-id type="integer" nil="true"/>
  <responsible-user-id>1</responsible-user-id>
  <status>active</status>
</ticketing-milestone>