Functionality needed for the first feature release

[geoffxy]

Required

• [x] Declaring a task instance
• [x] Adding a "runnable" task (i.e. run something)
• [x] Declaring task dependencies
• [x] Processing an execution plan with task instances and dependencies
• [x] Ability to run a complete execution plan
• [x] cond clean functionality
• [x] cond archive functionality
  • [x] Experiment versioning by git hash and date time (#7)
  • [x] Timestamp based identifiers (handle deduplication too)
• [x] cond restore
• [x] Release scripts
• [x] Tests (#6)
• [x] "Combine" pseudo-task

Nice to have

• [x] CI integration for tests, formatting, and type checking
• [x] Relative task identifiers for deps (#5)
• [x] Consider renaming .condconfig to a non-dotfile? (e.g., cond_config.toml)

Moved to next version

• Task aliases in cond_config.toml

[geoffxy]

Completed as of commit 049a85a95f30b6b6040e7b9674800f0d5b6a978e.