Make ACID compliant

[evanmays]

Should be possible with <20 lines of code.

Accepting PRs

[alexloi]

@evanmays does it make sense at this point to spin up a sqlite3 or dump things into a redis? Or you prefer keeping in code?

[evanmays]

@alexloi Ideally we can keep the idea of "database as a json file" for ease of use.

python std lib should provide everything needed for locking and whatever else is required for ACID compliance