Add support for multiple transition targets when using parallel states

[dimsuz]

If I'm not mistaken, this feature is currently missing from kstatemachine.

I'll use existing statechart implementations as an example (again).

1. In xstate.js having this state machine:

   {
   id: 'file',
   type: 'parallel',
   states: {
   upload: {
     initial: 'idle',
     states: {
       idle: {
         on: {
           INIT_UPLOAD: { target: 'pending' }
         }
       },
       pending: {
         on: {
           // NOTE multiple targets here
           UPLOAD_COMPLETE: { target: { upload: 'idle', download: 'pending' } }
         }
       },
       success: {}
     }
   },
   download: {
     initial: 'idle',
     states: {
       idle: {
         on: {
           INIT_DOWNLOAD: { target: 'pending' }
         }
       },
       pending: {
         on: {
           DOWNLOAD_COMPLETE: { target: 'success' }
         }
       },
       success: {}
     }
   }
   }
   }

   (sample transition above which has multiple targets might have a slight syntax or target specification errors, but it should work something like that, I tried before :))

2. In SCXML:

   <scxml>
   <parallel id="ButtonActivity">
   <state id="Button">
     <state id="BtnOff">
       <!-- NOTE here multiple targets states are specified separated by space -->
       <transition cond="_event.data == 1" event="click" target="Button.BtnOn StateShape2"/>
     </state>
     <state id="BtnOn">
     </state>
   </state>
   <state id="StateShape1"/>
   <state id="StateShape2">
     <transition event="on.released" target="StateShape3"/>
   </state>
   <state id="StateShape3">
     <transition event="on.released" target="StateShape4"/>
   </state>
   </parallel>
   </scxml>

   It would be very nice to have something like this in kstatemachine.

[nsk90]

Done in https://github.com/nsk90/kstatemachine/releases/tag/v0.26.0