Squashed commit of the following:

commit 73994327de890590eede353c8131f3f7c1e8aaa3
Author: Ian Roddis <gitlab@ie2r.com>
Date:   Wed Aug 25 13:38:29 2021 -0300

    - Fixing up checks for individual dag runs

commit f20e3a3dec8c063111cf60f2bec2b8f84c8a4100
Author: Ian Roddis <gitlab@ie2r.com>
Date:   Wed Aug 25 10:49:43 2021 -0300

    - Finishing serialization of DAGRun
    - Checkpointing work.

commit b490abadf93e3085e4204003de7eaa8183b4e1d5
Author: Ian Roddis <gitlab@ie2r.com>
Date:   Wed Aug 25 10:34:08 2021 -0300

    - Consolidating struct definitions into Defines.hpp
    - Renaming DAGRunRecord member runStates to taskRunStates

commit 050346ec1fd10d1091f261905c6175ffe0bcf001
Author: Ian Roddis <gitlab@ie2r.com>
Date:   Wed Aug 25 09:27:05 2021 -0300

    - Adding additional tests for server endpoints

TODO.md

@@ -6,8 +6,10 @@ Tasks
         - [ ] Add in authorization scheme (maybe PAM auth endpoint with JWT?)
         - [ ] Flesh out server and interface
     - Core Functionality
-        - [ ] Handle return on errored DAG / Task
-        - [ ] Clearing a DAG Task
+        - Allow `{{,!DATES}}` style interpolation, where values from `{{DATES}}` are preserved as a single, comma
+          separated list
+        - Allow for tasks to define next tasks
+        - Add execution gates
         - Executors
             - [ ] Slurm Executor
         - Loggers
@@ -22,4 +24,6 @@ Tasks
         - [X] Add ability to define child -> parent relationships
         - [X] Rip apart scheduler and re-implement runDag as a utility function, taking an execution pool, task list,
           and logger
-        - [X] Resume a failed DAG
+        - [X] Resume a failed DAG
+        - [X] Handle return on errored DAG / Task
+        - [X] Clearing a DAG Task