WIP: New Task Freshness Algorithm

[asg017]

Assume we are in a cellDecorator. The decorator is currently at a task, t. These are the steps we should perform to determine if the task should be re-ran (and why).

1. Create an input signature of the given inputs. For every dependency, if it is a task, get the filesignature of that task's targets. If the task has any "watch" files, get the filesignature of that as well. Then, hash all those filesignatures together, then save it.

CREATE TABLE TaskExecutions (
    run TEXT,
    cellName TEXT,
    ancestorCellHash TEXT,
    dependenciesFileHash TEXT,
    freshStatus TEXT, -- "out-of-date", "up-to-date", "does-not-exist"
    runProcessStart INTEGER,
    runProcessEnd INTEGER,
    runProcessExitCode INTEGER,
    runProcessPID INTEGER,
    expectProcessStart INTEGER,
    expectProcessEnd INTEGER,
    expectProcessExitCode INTEGER,
    expectProcessPID INTEGER,
    outputFileHash TEXT,
    runLog INTEGER,
    expectLog INTEGER,
    FOREIGN KEY (run) REFERENCE Runs(hash),
    FOREIGN KEY (log) REFERENCE Logs(rowid)
)